Only XBLA and indie games run in managed C# using XNA, since Microsoft wants some sort of protection against running full unsigned code on the device (which makes the xbox the only console that hasn't been completly rooted).
Also, AMD can suck it. The reason for PC games to look the same as the console versions is not the fact that developers hate directx or opengl apis, it's the fact that it takes a buttload of work to make content in higher resolutions for PC only. Content budgets are already sky-high, and making higher res textures, models and shaders just for PC isn't financially viable for a platform that has such a high percentage of piracy.
tl;dr: Content creation for games takes a lot of resources, and developers really don't want to make everything in higher resolutions. They don't care if there is an API in the way, you don't need direct access to the video hardware anyways, and most stuff is already accessible to make hacks like carmacks reverse technique for shadowing.