Because I have a ATI Readon HD 5670 X2 vid. card, ati and openGL have problems with each other (often)
yeah it's pre-rendered but I always imagined how they did it, is it like drawing ( as in animated movies such as: shrek (poor example) ) would be so nice to know how, not that I even try to make it myself... because I will use another method as: just use a green-screen and some advanced filters to make it appear such awesome.
still the fact to implement DX11 or let the user choose. is so much more user friendly.