In my case, its not so much that I need millions of choices, as I need one specific choice, and if that choice doesn't exist (or "exists" but is blatantly mechanically inferior), I will never enjoy the game.
In my case, that choice is the option to play an intelligence based spellcaster whose powers are inherant (or psionic equivalent, in sci fi games). Basically, a nerd whose nerdiness directly corresponds to an intrinsic (meaning, not related to gear) ability to blow people up, and who does not rely on the gods for help.
This is because I play RPGs to act out wish-fulfillment fantasies, and I'm an atheist nerd who primarily fantasizes, not about being something *other* than an atheist nerd (like, for example, a brawny, musclebound star athlete or warrior), but about situations in which being an atheist nerd makes you teh awesomest (obviously my favorite Dragonlance character was Raistlin).
If effectively contributing to a game requires that I play a character whose effectiveness is either tied to physical aptitude, or to faith in some diety, then that games fails as wish fulfillment for me (which is why, for example, I don't play Iron heroes).
If I was the only gamer on earth, then the only class D&D would ever need would be wizard.
But I'm not the only gamer on earth. And the thing is, lots of other people have a completely different archetype which is their "one choice" that they have to have. Rogues and fighters and priests sure, but you often find even more granularity than that. Players who just have to have nature themed powers, players who need to use spears, players who specialize in fast-talking. There are a nearly infinite number of archetypes, and if you look long enough you'll find some gamers who simply won't enjoy a game unless their archetype of choice is supported.
So, in designing a game for a wide commercial audience, you need lots of choices, so that guys like me who aren't having fun if they aren't playing Raistlin can have fun, and so can the guy guys who only enjoy playing Conan.