D&D and Rules Mastery

The thing is, the core rules in D&D 3rd Edition are actually fairly simple - roll d20, add modifiers, try to beat target number.

The bugger of it is the details. In the Player's Handbook alone there are stacks of feats and hundreds of spells, all of which do subtly different things. And you don't just need to know what they all do; you need to watch the combinations as well.

Now, in an ideal universe, the players would take a bunch of this off the shoulders of the DM. If every player can be relied upon to know everything about their character, to keep track of exactly what bonuses stack and which don't, to look up every spell before they cast it, and so forth, the DM wouldn't need to worry about such things.

However, many players just don't know the rules (and I'm not making a value judgement here - not everyone needs to be as anal as me), don't think to do these things (looking up spells or tracking ammo), or are just plain cheats (oops, I forgot to mark off those magic arrows).

This isn't restricted to rules-heavy games, either. Have you ever seen a character, in any game, ever stop to reload his shotgun? I haven't, yet these weapons typically carry the smallest number of rounds of any firearms in the game, or at least any that are used.