It depends on both card and drivers. Reason why ATI have poor drivers is because the card is ultimately designed for DirectX as a primary engineering design. OpenGL support is nothing more then that, support. nVidia on the other hand, design there card for OpenGL as a primary engineering design. nVidia make a good deal of money off providing cards that work for large scale rending and designing tools that are packaged together, such as Maya, which works and is often used in UNIX/Linux from it's old and expensive predicessor, the PIXAR. In addition, many buyers of computer systems that do graphic design often get Macintosh, which often goes hand to hand with a nVidia graphics card, since Macintosh lagacy (Mac os 9.x or less) and the new OS X (UNIX) and Jaguar (Linux) support OpenGL.
Never-the-less, OpenGL is, IMO, far superior then DirectX. To add, Linux is far superior then kernel32 (Windows). When you add the two together, they make a superior OS. Compile a game directly onto that system, and you will see a better design then that found on Windows. As Taylor expressed, he does not associate to much with WineX. This is a good thing and a bad thing in his position. The good thing is it makes the design of FS2 for Linux far more powerful, since it is working directly with Linux. But it is also a bad thing, because it takes a lot of work. There are things known WineLib which do make life easier, but if the code is altered enough to work directly on the Linux OS without the winelib, the compiled program would be far better.
One example to what I'm saying is Neverwinter Nights. The program was designed for Windows, but was also compiled with WineLibs. Dispite the Wine libraries installed, it works better and more stable on Linux then it does on windows. If the program was designed to work for Linux without the wine library, it would be even better.