You've always been able to run Ubuntu on Windows since the XP days with
WUBI, a Windows installer which has been on every installation copy of Ubuntu since 2008. It installs Linux as just another program running in Windows. You get none of the security advantages of Linux, it slows down Linux so you would think it was slower than Windows when actually it is more than twice as fast.
They are just defanging Windows enough here that it will tolerate another operating system. Probably an anti-trust move more than anything and I'm not happy that Canonical went for it. Windows needs to be attacked, not coddled and encouraged in its monopolistic jihad.