1. I think many of the old ones are too old to update. Some of the new ones perhaps.
2. I just finished one. Although it's for XP and Vista as well.
3. As John mentions about supporting 3 OS's, this is one of my griefs as well. I can manage 2, 3 is a bit much. Yeah, I'm lazy, but I also support progress and would love to see people move away from XP to something new and modern. There's a ton of time consuming bits to XP skins that are annoying to do.