xvba can decode h264 up to l4.1 but not l5.1. That means when you have got bluray m2ts you can play em but not videos encoded with a higher level.
It's been stated several times on this forum and others how gfx cards work. One of the main problems with computer graphics is the amount of gray areas that exist (read: the features and functions that aren't explicitly defined/covered by the specs). People who follow graphics technology have acknowledged this. Developers have acknowledged this. Hell even bridgman himself acknowledged this. All we can do is hope DirectX 11 games work better with ATi - seeing as how they had DX11 cards a full 6 months before Nvidia produced one.
had to do some googling, as i've never actually seen anyone pose that question, or comment on the subject of it.
but the impression i got from reading on the wine mailing list some was that the situation for intel cards is much worse then the one for AMD ones.
which isn't really suprising.