Even a casual gamer would know these things after only a couple months of playing.
Actually, no. And I've already covered this. Now, your definition of "casual" may be different than mine... but I've known plenty of "casual gamers" that didn't and they didn't care to either.
It really isn't hard and there isn't a lot to remember, d20 is actually an extremely easy system. It was designed to be easy and they succeeded.
No. I don't want to threadjack this thread, so if you wanna discuss this I'm willing to post further in a different thread, but... you're wrong; it wasn't designed to be "easy". It was redesigned to unify mechanics that previously had multiple different subsystems, but it wasn't designed to be "easy". It was designed to be more unified.
In fact, d20 was explicitly designed to force system mastery. Monte even says so (although he calls it "rewarding" instead of "forcing"):
Ivory Tower Game Design
The d20 system is actually quite complex. It has a relatively unified mechanic, but the whole game is based around exceptions to the rules (sharing similarities to Magic:TG); that's the function of most of the Feats out there. You start messing with things and you've got multiple cascades of things happening.
Often times a unified mechanic makes things easier, but it doesn't actually make something easy. Heck, that's a fundamental part of what this thread is _about_ in the first place: there's a unified mechanic (Ability Damage/Drain) but the application of it is a pain in the rear.
Look at airwalkrr's post: He's got a fairly unified mechanic that simplifies the degree of Damage/Drain that occurs; but he's still hitting ability scores. Which means that the severity of the effect might be reduced, but there's still going to be recalculations required. In fact, if a group is unlucky, his approach might mean a character has a higher survivability and it's simpler/faster for the GM to inflict the damage, but a player might actually waste _more_ time, having to refigure things more frequently; yeah, their character lived, and instead of being reduced to 0 in a couple of hits, the combat is dragging out and that means more instances of refiguring things.
Simplification/unification/streamlining does not automatically equal "easy", though it can mean easier in specific situations.
Note: I'm not saying airwalkrr's approach is "bad" or "wrong" or whatever. I'm simply pointing out that his approach may address some issues that some people have, but in and of itself it doesn't actually address what people like myself don't like about the current way that Ability Damage/Drain functions.
My previous example of a generic stacking penalty [-2 to all dice rolls], possibly combined with a Hit Point kicker [5 HP damage] is a much "easier" solution that doesn't require refiguring everything and is still "unified" as well.
Of course, combat is still going to slow down because part of combat length is dependent on character capability; so as you reduce the character's capability, you increase the amount of time it takes for them to be effective. In other words, if you reduce a character's capability by half, it's going to take them twice as long to create the same effect as if they were unaffected. That's an additional effect of this whole thing that we're just not actually talking about.