Perhaps, Brad, but then again.... when skinning was still in the cradle people hadn't "settled down" with their fav applications. We saw new applications jump out of the woods, so to speak, all the time. New and better applications and perhaps more challenging.
People have now found the applications they wanna use + are leaving the skinning to the hard core of artists.
I believe that is what has caused the slowdown in skinning.
We never see any new applications emerging anymore, that have the abbility to challenge what is already available on the market.
I think it's because widgets have eaten up lots of other categories. A skinnable clock? A skinnable calendar? A skinnable weather monitor? Widgets have taken over those things.
I mean what were the really popular skinnable programs of old that have died out in terms of skinners? The shell themers have definitely taken a beating over the years (Aston, ObjectBar, WinStep, Hoverdesk) but in terms of other programs like Winamp and Media Player, I think one thing that has hurt is that iTunes isn't skinnable and so many people use that now or just make widgets for controlling media players instead.