Even if the majority of games became "dumbed down" in some way (however you define that), I think that an attempt to make them more acceptable in mainstream culture (or else how are they suddenly mainstream?) would result in many beneficial eliminations of the more tedious aspects of the genre, and not significantly depreciate the positive elements. Additionally, I think that more complex games could still exist in much the same way that - while there are more than a hundred FPS games a year - you still get excellent or at least intriguing games like Braid, Bastion, Limbo, Minecraft (I'm told), and more, none of which I feel carry a terrible stigma that I think many people still associate with the tabletop genre (and which I think this thread is addressing), even if they aren't all decidedly "mainstream."
I'm not convinced that complex rules are what make these games valuable - or that the burden of such rules should be placed on the players, at least. I'd argue that a very well built tabletop RPG today - assuming it doesn't simply seamlessly integrate itself under the guise of a multiplayer computer game, which I think is still the smarter option for gaining acceptance - could be done while not exceeding the 15 pages LordBlades gives as an example, at least for its core rules.*
*I will acknowledge that accounting for individual abilities characters can gain may cause the page count to exceed this, though systems can use some abstraction to avoid this altogether, but I think all of the truly essential rules of a tabletop can be presented in 15 pages such that all individual abilities make sense in context of only those pages (or possibly an ability that is prerequisite to another ability).
For this discussion, in what way is it essential (if you feel it is) for players to not only be willing to but not be disgruntled by having to read hundreds of pages to play the game? Is the reading and preparation more essential to the enjoyment of the game than the act of playing or the group (and social dynamic) with which the game is played? If so, why?