To turn the logic around here. If MS should feel obligated to make sure all its software works on windows XP, then shouldn't web developers continue to feel obligated to make sure all their websites work on IE6?
The point I am making is that this logic doesn't work, MS has no obligation to make IE9 run on XP. MS continues to release patches for both XP and IE6, and that's all the obligation it has in terms of support. They have no obligation to release new browsers for old operating systems.