Let's just sum this up shall we.
1) XP, regardless of any ones current setup, was a rock-solid, well preforming piece of software and I think most people in this thread acknowlge that fact.
2) Windows XP has had a long and wonderful life.
3) DX11 will NOT run on Windows XP
4) Making a game work with DX9, 10, and 11 is NOT just adding "a few hours of code" that's like saying that if someone writes a book in English, they only have to type up a few more paragraphs to make it readable to Japanese.
5) Windows XP (the GOOD version anyways) is a 32-bit operating system, this severely limits what can be done from an architectual point of view for games, along with limits like the ~3GB of RAM.
6) Gaming publishers should NOT have to go out of the way to support a dying OS. Can you take your '86 Civic into your local Honda dealer and get warranty work done on it? No, you can't, because it's illogical to try and support something that is far beyond it's prime.
7) Just because you think that XP is the greatest thing in the world and are too ignorant to give a new OS a fair chance doesn't mean that you have the right opinion.
8) If you can't afford a new computer, you probably shouldn't be spending money on a $60USD video game. Instead of getting the next game you want, put the money in a little jar labeled "Gaming Computer Fund." For less than $600 you should be able to build you a fairly decent rig.
9) If "your parents" can't afford or won't buy you one...just GTFO
TL;DR Anyone who has XP and doesn't upgrade will soon find that their game library will stop growing, end of story.