3. Modifying the CRT to run on XP is a very simple process. If it takes a single Microsoft employee more than a few hours, then that person is just incompetent. But surely the reasons are the high managers making their weird decisions. I just hope no one comes up with a stupid "no resources" argument.
Even if you modify the CRT so that it only uses calls available on XP, most of the Windows headers in the current SDK don't support XP, so you still couldn't use it without a massive amount of effort going into ensuring all the header files are compatible with XP.
It isn't going to happen.