If so many Win32 developers care that their program runs in Wine (they must if it's an excuse for using Win32) they would test their programs to insure they run well in Wine. Given the volume of programs that are still quite quirky in Wine... kinda hard to buy it.
What if Steam and all its glory comes to Linux? Why wouldn't they just improve how Steam works in Wine? Given how poorly the Steam client runs in Wine, I don't think they're looking at it much.