I really think celphones will be the first platform to abandon 2d games.. I just dont see much... loyalty if you will to 2d gaming and as soon as the resolution standard is bigger and more capable technically, I think 2d games will completely be phased out.
but, I cant remember where I read it exactly, but an interview with miyamoto and he said he doesnt want the next gameboy to be very powerful because he wants most games to be 2d. and I dont think capcom will drop making streetfighter in 2d, same with metal slug
1 - Because mobile phones were not built or designed for games, just a handy extra - pixels only provide the simplest form of a game with very little memory used, and as soon as they can advance - they will.
2 - That's why you gotta love Capcom. Founded on that style, the 3D EX series of Street Fighter was even boycotted by some fans, it just wasn't the same and that of SF3 and it's two additional games after that were hits. There's no way aswell people would consider Metal Slug as anything but sprites.. though, cracks at getting these types of games on new gen consoles have been rather poor - sticking to 'Nintendo' based or handheld consoles are the best bet.