I found an interesting post on 'The Alexandrian' the other day, that I think speaks to the point of this thread.
The Alexandrian (see 'Opening your gaming table')
Basically, he writes that a roleplaying game can be liken to a game of baseball; when he started with megadungeon-type games, the commitment required, in terms of time and effort for the players, could be likened to a game of catch. In other words almost nothing. They got together, did a delve and if the same people were not around next day, (he played in school breaks, as did I) then it was no problem.
Now, with games that rely on huge story arcs and loads of plot, each player becomes integral to the game, almost from the moment they join and so they are signing up, possibly for several years of weekly gaming.
His point is that a hobby requiring that level of commitment up front, is analogous to asking someone who is about to join a game of catch for fun, to commit themselves to the baseball leagues right from day 1.
It just doesn't sell well with many people.
I was also thinking something similar when I was hauling out all of my 3.5 books for a game a few weeks ago; looking at the vast amount of rules we need to play this game, it must really intimidate the newbie gamer. I mean I had 30 books on the table at one point. Even the 3.5 PHB is a heck of a lot to learn.
Note that computer games do not do this; they are essentially 'fire 'em up when you want' games of catch and you don't need to know any rules. So they remove both the social and the rules knowledge constraints from gaming.
Hence they are more accessible.
So if someone wants to make TT RPGs more accessible, I think they need to produce a game that is episodic in nature, where the cast can change every session and that is rules lite.
But also make this rules-lite game one that has the same intrinsic rules as something like D&D, so that the more interested gamer can slowly graduate if they want.
I guess this also suggests that we, as DMs, need to think about running this type of game when we first start up in a new area or when we are trawling around for new players.