Paradigm is a word used by snubs Managers /end snubs to describe something they don't understand
That said ... before XP, and all the ... security features read bugs they had a 2.5yr turn around on Os's
XP, and now Vista are so bloated, that it's a mammoth task to improve on it.
Probably takes several months for new programmers to get upto speed on the existing code, before they can contribute
And they'd have programmers leaving ... ouch!
I think 5yrs to improve on vista may be well short of the marks.
New OS's may likely just be updates to the interface, rather than any serious overhauls of the underlying system