It isn't an oversight. It is a deliberate move. Windows XP is over 10 years old. I personally feel Microsoft has done a great job of supporting Windows XP as it is now 3 OSes behind current version. Mainstream support ended in 2009 yet they have still released major updates for it. Windows XP is now in extended support which just covers hotfixes basically. With regard to orgs not adopting framework 4.5 due to it not supporting Windows XP, I've actually seen that as a pretty good pressure point on management to finally upgrade those machines to more current OSes.
The best way to accelerate a Macintosh is at 9.8m/sec² - Marcus Dolengo