Yes, but it is not the Microsoft version of the API. Sure it is close, but not everything is 100% perfect and probably never will be. As such the behavior is not identical to Windows. It works, and in many instances it works great. As you said it is a library that calls other Linux system libraries, its behavior is directly linked to how those system libraries behave. With Windows you have a small subset of behaviors to look for. There is Windows XP, Windows Vista, Windows 7, and possibly some of the various Windows Server versions. With Linux there are so many distros and so many permutations of libraries I can see it being nearly impossible to correctly identify them all as WINE. Blizzard is looking for people who have altered libraries and effected system behavior for the purposes of cheating. The game allows you to sell items in a real world auction house. As such they have to protect their investment, or a bunch of people with server farms could farm items and flood the market with powerful items for shit money. Blizzard said flat out that they were going to be very strict on cheating so it does not surprise me that systems that are not behaving like a perfect version of Windows are getting banned. They were very explicit in the list of supported OSes and Linux with WINE is not one.