morningstarrising, good point, yet...
They could just have built a new OS in secrecy, and when its ready, implement it, and itd have full legacy support without the weaknesses. Isn't that what Apple did with OS X for last five years?
AFAIK, Vista isn't a new slate; its just yet one more update on a husk of dead corn.... I suppose M$ has their heads so far up their asses, they can't find the way out....