I use WIndows XP inside a virtual machine, running on top of Ubuntu. I don't like Windows, although WIndows 7 is almost OK, and I don't want to sink any money into a system I don't want to use. I do like many old games, such as Myth, Thief, Total Annihilation, The Neverhood, Starcraft, and even Dune 2. Old games, even those that are most demanding, can probably run on my virtualized Windows XP, so I'm not forced to dual-boot in order to play them, plus I'm willing to spend money for stuff that has nostalgic value. However, for games that aren't childhood favorites I will only buy native Linux games. I wouldn't get a new non-Linux game unless it was free.
On top of all of that, my best computer can't even play Achron, Overgrowth, or Amnesia, and might not be able to play Trine or any of the most graphically demanding indie games. I still buy them since I know I will eventually buy a much better machine, but that means I wouldn't be able to play AAA games for the time being anyway.