I had many instances of the "Low on Memory" Windows7 warning. It was not breaking the game, meaning that you could typically ignore the warning and keep on playing without anything going wrong on the game or the system. Those came up when I had only Firefox (3-4 pages) and Steam running, apart from the game. As I said before, I know the game uses complex shaders and stuff, but it's just a pixel game, come on... When I play 3D games like Skyrim or Bioshock Infinite, at decently high settings, I need to close everything down, and I still get some "Out of Memory" (non-breaking) warning; but, there, it's perfectly understandable!
*** My System: Win7x64 // 4GB RAM // 2.83GHz Core2-Quad CPU // 1GB HD4850 VGA.