The history of operating systems is based on the constant revision and perfection of existing operating systems. Allow me to give several examples.
There are many Apple fans here that are screaming Vista at Windows 7. In what way, then, is Leopard a massive leap from Tiger? Tiger a leap from Panther?
The explanation for these incremental releases is simple: Apple has a stable codebase with the OSX core, and now they are constantly seeking, in small ways, to make it ever so slightly better.
The features introduced in Leopard over Tiger are nothing compared to the features being introduced in Windows 7. The Superbar is a massive paradigm shift in windows computing, take it or leave it. Vista now has a stable, reliable core codebase. Their priority now SHOULD be improving what they have, removing what they dont need, making better what they can make better, faster what they can make faster, and easier what they can make easier.
Might I add another point for the consideration of Linux users. I have has Ubuntu as my secondary OS for quite a while, and many KDE based distros before that. And every time a new release of these desktop environments or distros was released, they garnered much praise over older versions. Until things went horribly wrong with KDE 4. KDE 4 IS a massive shift over the previous 3.5 series. But that is not appealing to the users, when instead the users said that they should have instead focused on IMPROVING their current line of KDE - not starting from scratch.
It is even more evident with GNOME. For years, GNOME has not released a major rework of their desktop environment. Instead, they have made it sleeker, faster, and prettier over time.
So what, may I ask, is the problem with Microsoft doing the same thing?