I have both PC and Mac workstations I can tell you I 100% think mac is better than windows in many areas, and windows better in other areas such as gaming. But Microsoft does not need to bloat the price of Windows because c'mon windows is not worth $400, there should be 1 set version for $130 or even $99. The only reason why Mac OS X is at $30 because at this point it's just new features added, supports the latest apple approved gpus which are the latest from AMD I believe it's 6X now, and uses intel as I honestly can't stand amd cpu's but love there gpus :p
I don't like windows but I use it for game creation and that's about it, everything else I'm on either using mac or arch linux(the best flavor of linux).
If you guys went with OpenGL you could target windows, mac, and linux users as all OSs support OpenGL.