Do they? Is it the same market that would have bought the game? I find that the people who complain about that were never going to buy a 2d platformer in the first place. I've never met someone who has said 'I would've bought this sidescroller if it used actual polygons'. Sure, there's people who want a 2d side scroller to be 3 dimension, but they mean in all ways not just the graphics.
Do people see movies like Princess and the Frog and say 'why isn't this cg? This is outdated'. I really don't think that 2d or 3d matter in these kinds of games.
They absolutely do. Anecdotally, I have heard people say that exact thing.
And even Disney picked up on that. Pooh was basically not marketed at all and the amount of traditional animation since Princess and the Frog has been anemic, at best.
I know people who are hardcore gamers that do not believe sprite-based fighters should cost as much as 3D ones. To them, $60 for Persona 4 Arena is insane because it should cost more like Skullgirls.
Epic Yarn got a lot of the "Why is this a retail title when it would be downloadable on any other system?" bullshit in threads here and among some gaming journalists.
The "CG is just plain better" mentality is pretty common in the mainstream. It's flashy, it's colorful, it's not early 90s, the market is more willing to spend money on it.