Last night a friend said something to me that I think sums it up exactly:
"Before, everything was ugly and gray. Gray windows, gray buttons, etc... But now, eye candy is everywhere!'
And that's the thing we 'old timer's' have a hard time realizing because the change has been so gradual: in those days, basically nobody in the world of Windows cared about aesthetics. We were mostly techies, applications had to be functional, and nobody cared how they looked!
Take the original WinAmp skin, for instance: how ugly was that compared to what came after?
Anyway, all this changed with Apple and Steve Jobs. The guy had 'taste', unlike Bill Gates. That's why skinning had it's hugest boom with Mac OSX and the will to make Windows look more like Mac OSX.
Then Vista/7 came and two things happened: Vista/7 had tons of eye candy, which in turn prompted the visual quality in most apps to rise as well. Suddenly eye candy is everywhere, as my friend said - and since things are no longer butt ugly, the need to skin everything and its dog all but disappeared.
Even Windows 10, which we like to think of as butt ugly, is an order of magnitude better than XP in the looks department. 
