I was searching my long list of bookmarked webpages earlier today and came across this entry from Corvus Elrod’s Man Bytes Blog. In ‘Amnesia Alternatives’ Corvus outlines two ways that a storyteller (read: anyone setting up their game) can overcome the initial barrier to a players knowledge that a brand new world they’ve never experienced presents.
It's unreasonable to expect every player to read a hefty manual explaining their character's back story, or worse—to subject them to a lengthy game intro which delays their entry into the game itself.
So dumping the player into a situation where they know nothing about the character or world is a perfectly reasonable means of setting them up to learn things within the game narrative proper.
He suggests two approaches, the first is “Relocate the player”, that is, have them start in an area that actually is new to their player as well. The second approach that Corvus suggests is to start the player as a Child or as “child like” characters, which also seems a very untapped alternative. There really is very little excuse for the “amnesia, lol” approach, if there ever was.