Mouseferatu said:
The fact is, most people don't tweak the magic-using classes.
I think you'll find the real fact is that most people sit and watch TV, and don't even play RPGs...
All sillyness aside, do you have market research to back that up, or is it just a suspicion? Because as I understand it, D&D has always been a game rife with House Rules. 3e, 3.5e, and the new Unearthed Arcana are in large part products built out of house rules. Even if the majority plays the game straight out of the book, the minority that doesn't is sizeable, and not to be dismissed.
Plus, the majority playing it straight also stands as an argument against you. If it isn't so bad that people are changing it on their own, why change it in the core book? If you could actually tell me that it was annoying enough for most folks to change it on their own, I could see some validity in your position. But if the majority like it well enough as-is, who are we to change it on them? Why kill the sacred cow if it isn't standing in the way, or is at least easy to shove aside?
Don't get me wrong, I don't think it's bad the way it is. I just believe it would be better--across the board, for purposes of flavor and imagination both--if they went one way or the other. That, IMO, would actually provide
more flexibility than we have now, not less. Fuzzy definitions aren't the same things as options.
Fuzzy definitions are not options, true. But they are sources of inspiration.
The more distinct, flavorful and unique you make a game element or mechanic, the less likely people are to muck with it, and the more difficult the task to rewrite the thing becomes. Integral and strongly unique systems are apt to either inspire devotion, or make you put the game aside completely.
Elements that work well enough, but aren't exactly gripping either instead tend to invite you to change, tweak, and play with them. Leaving some of the core rules a little bland is good for the game - it drives the d20 and OGL market, and leaves room for books like Unearthed Arcana. If you really want options, you don't more strongly define the core, you publish optional supplements.
So, stop thinkking like it's the TSR days, or like you're a White Wolf player

Leave the core vanilla (and leave it with it's sale-generating, product identifying comfortable sacred cows), and allow the third party publishers to play with more specific stuff. That's what the d20 license and OGL are for, darn it.