I'll agree, to a point, that games that start with advanced characters tend towards power gamers. Lord knows in college most of the games the powergamers loved were like that.
However I think if you actually played from low to high levels, the complexity isn't a problem for the players. DMs, well, some DMs just don't do well with the challenge, but they face it from a mechanical and plot standpoint. Many DMs aren't capable of putting together 20 levels of plots without having them fall apart. I suspect that few games cross the 50-session barrier and wouldn't be surprised if the vast majority die within a dozen sessions.
I think a lot of the perceived problem with high level play is that DMs are often jumping in the deep end of the pool and having a bad reaction. "Ooh, a module for characters levels 15-17. Sounds fun, I'll call the guys." Then during the session the players pull out powers the DM's never noticed and therefore doesn't have a response for and feels that high level play is unbalanced.
I applaud the adventure paths as the best way to ease DMs into a long-term game with good potential of reaching high levels while providing the hand-holding needed.
Personally, I think that a DM who doesn't railroad won't have much trouble finding plots for their group at high levels; most players leave a trail of half-finished quests and escaped villains that almost always have some repercussion that can be laid at the party's feet. The railroaders are the ones who have the most work to do, since they never let the players deviate from the plots.
