I ran smack into this problem ... the 'why be human' question, whenever I wanted to change the class level limits.  Humans had very little to offer, and this was the game's offering for why to be human.

Then, a year ago, I established my mass = hp system and solved the problem.  Humans are more massive, and therefore start with more hit points.  At once I created a justification to be human no one had thought of, and made my demi-human party members happy by getting rid of the race limits.

As an aside, I did tool around with reducing the amount of damage done by non-humans, again on the basis that a halfling would use a smaller 'sword' than an elf, and an elf a smaller sword than a human.  It did work to some degree, but the mass thing worked better and I got rid of the weapons ratios.
                

                
Thanks, Alexis.  I remember those posts and I'll go read them again.
                

                I read through it all, and man it seems like a doozy of a project, but rather neat to see the overall results if you can actually accomplish the total conversion.

Alexis, 
Did you ever implement all of those changes in your system, and did you have to change all of the monsters in the process?

I like the take that players move on to be superheroes as they level. It seems to me that you either view the game this way, or you should just try some other gaming system where there are no levels.

The problem with class level limits seems to be that the effects aren't going to be felt until much later in the game. So to a player, it probably doesn't feel like a compromise until you reach a point where it's time to retire and roll up a new character. I too get the premise of allowing a tradeoff between benefits and level caps, but it almost seems like an apples and oranges comparison.

It seems like it would make more sense if humans lived longer, then you could say that they have time to specialize, but the situation is reversed, so how do you justify that? Of course, it's just a game. But I've really yet to see a good fix other than "play a different game." Thus take it or leave it, I guess.
                

                
Nick,
Alexis did have to change his monster manual to account for the mass to hit points rule.

Alexis,
Correct me if I'm wrong.

Nick,
I'm going to go with play-the-game-as-written, however, that's not really the spirit of AD&D.  The rules are a starting point, a common language given to players and dungeon masters to allow them to communicate about and play within each other's games.  Beyond that, it's up to the group playing the game to decide what's right for them.

There's been a lot of talk within the revival of the Old School movement about what Gygax wanted and how he envisioned the game and so forth, but the more of that I hear, the more I think that crediting Gygax with D&D is like crediting Noah Webster with the English language.  Gygax (and many others) codified something that had been in the works for years prior to the publication of either of his D&D game systems.  D&D is the language he wrote to describe it, but like any language, it changes and evolves over time and is changed by the people speaking it.

That's what I'm doing here.  We all know the language, but there are phrasings and words I'd like to have agreement upon before we start composition.

The problem with racial level limits is that aside from giving people a reason to play humans there seems to be no reason for it, just as there seems to be no reason that humans can't multiclass aside from giving people a reason to play other races.

So, Nick, I think you're right about playing the rules as written.  There's a reason, and it may not be very good, but without it, we'd end up with a game of all elves, because they live for 1000 years.

I am going forward with the premise that humans can breed with any demi-human or humanoid.  This should allow a little more latitude in the class restrictions (allowing half-halflings -- farthings? -- to be clerics for example).

I'll further add in that demi-humans with prime requisite ability scores over 18 will be allowed an additional level over their max restriction in the book at a ratio of 1 to 1, so an elf with a 20 strength would be able to achieve 9th level as a fighter.  If that elf managed somehow to attain a 25 strength (the AD&D maximum for ability score) he or she would be able to attain 14th level.  If that doesn't sound right, I'd love to hear why.
                

                I have not upgraded the entire beastiary ... though I regret not doing it while I was free from work.  At the moment, I am calculating monsters as I use them in actual running.
                

                You might take a look at the avatars for the various demi-human deities and see what their level limits are.  My thoughts being that any individual exceeding these might be on their way to becoming the new avatar for said deity.  That could open up a whole new level of play on the planar levels later in the game.

The other thought could be setting the max level for unlimited classes to be a level or two below what the deity's avatar has achieved.  This might require a more exponential determination for levels points beyond 18 or maybe a cap that kicks in, no matter what the ability score is.
                

                "If that elf managed somehow to attain a 25 strength (the AD&D maximum for ability score) he or she would be able to attain 14th level."

I can see certain classes with limiting your level by your stats, but the (spell classes) are based on intelligence and wisdom rather than brute strength.
Why penalize them with a strength level cap, that would make it way harder for say a cleric to reach level 14 if they have to obtain Str. 25 as well.     

A Humans max strength is 18/00 Un-enhanced.

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Now, I'm looking at the Deities and Demigods handbook and a 25 strength gives a +7 and +14 tohit/dmg bonus and is considered 100% Titan strength.

That would benefit for Fighter/Ranger/Paladin(?other stats might be more worthy)/Monk
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In the PHB the levels that are obtainable are.

Illusionist at 26 
Magic User 29, 
Cleric 29
Druid 14
Fighter 11
Paladin 20
Rangers 12
Thieves 17
Assassins 15
Monks 17

Yet, on page 19 the top chart shows that only Druid/Assassin and Monk are level capped, all other class levels are not limited. Assassin is at lvl 14 which contradicts the actual lvl 15 on page 30.
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If you level cap 14. these classes can only cast up too.
(Before racial and int/wis/race modifications).

cleric- 2 6th level spells
Druid-  3 7th level spells
Magic User- 1 7th level spell
Illusionists- 1 7th level spell

And these would only be achieve-able if you also reach str, or wis, or int at 25. So my question is at what point do you start basing class levels on your attributes?

Would it be fore example, for levels 1-4 you need up to 10 Int, 4-8 up to 18, 9-12 up to 20, then 13 to 14 up to 25?







                

                @Craig - The example for the 25 str is only relevant to the elf's fighter class.  What Carl was saying normally an elf is capped to 7th level in the fighter class, but with a str score of 25 he would allow the elf to gain a fighter level of 14.  An elf mage is normally capped to 11 but if that elf had an int of 20 it could go to level 13 a max score 25 in int would allow the elf to go all the way to 1evel 18.  The elf's str score would have no bearing on its level cap for mage or cleric.
                

                This is failing to take into account that one page before, or one page after (can't remember) the Player's Handbook gives LIMITS on what stats non-humans can have.

25 strength is right out.

Ah, what the hey.  I don't use the race stat limits table either.
                

                Craig,
The elf fighter with the strength was just a single example to illustrate the concept.

Jason,
Thank you for the clarification.  You nailed what I was trying to say.

Alexis,
I always assumed the racial ability score limits were for initial stats only, but regardless that's how I'm going to use that table.  Wishes and other magical means can increase a character's stats beyond those maximums.  It was by those means that I figured players would get their ability scores increased.