Running Guild Wars with Wine on Ultimate Edition Ubuntu 64-bit, used Winetricks to install it.
It's not that you can't play Windows games on Linux, it's that people who only use Windows are noobs and will never know how to use Linux. Windows games installed with Winetricks actually perform better than they do on Windows because they don't get defragmented. Online games perform better because Linux has a built-in firewall that uses very little resources and you don't have to be running antivirus and antispyware apps that use resources. Linux also handles your Internet connection much better than Windows so you don't have bottlenecking and can play online games while browsing the web, downloading or torrenting if you have a broadband or better connection. Long story short, Ubuntu is perfect for gaming, but for to noobs who've never bothered to learn how to use it. On top of Winetricks installing games so that they play better on Linux than Windows, just about every system is emulated on Linux and all the good emulators have a Linux port.