To maintain neutral in Fallout 3 you had to steal a bunch of stuff and give water to beggars and keep doing it. It really wasn't worth it.
That is, indeed, true, and this seems to happen in some other RPGs which feature such a system as well. I think a lot of games just assume that you'll want to be either good, or evil, and treat neutral as just a starting point for when you have not yet done enough to go either way. To maintain neutral karma, you often need to randomly alternate between good and evil acts, thus, a neutral character seems not so much like someone who has not taken one moral standpoint or another as someone who has some sort of mental disorder. Not to mention that where as such games often give specific perks to good or evil characters, neutral characters often get the short end of the stick, so to speak.
Hopefully New Vegas will feature more options for a neutral character, my characters might not end up being neutral anyway, but having more room to act like such a person would be nice, if I want to play a neutral character, I want to be able to act that way.