Really depends. For instance, one of our players is 65 and always forgets what his character can do, how to make some rolls, etc. He's quite smart, but he also drifts off sometimes while waiting for his turn (we've got a HUGE group of 8-13 people a game). Another player can only make it sporadically, and he's busy with work so he falls asleep sometimes. Keep in mind it can take 20-30 mintues to get back around. We have to use miniatures becaues of that.In a way I'm hoping by sticking to one system for a long while, I can catch the two people who can't/won't buy in with time. At least, if we do a year of this at the table, that several hours exposure to the rules. So...should be some absorption, right? Right?
Conversely, one guy can't make it all the time, doesn't have the books, but he just remembers stuff.
Depends on your players.