Xfce default is not vetted by Debian release managers. Joey re-added it because he was thinking that no other upload would be needed. However, an RC bug popped up, which had to be fixed, and I could not leave the “XFce default” change in the same upload, as it would then not qualify for wheezy.
In short, I very much doubt that Debian wheezy will have Xfce by default. It will have GNOME if nothing changes.
I have never tried Debian and I don’t know either how versions or Tasksel work there. I just installed a Wheezy Beta 3 (Netinst Image) in Vbox and it works like this:
By choosing Desktop Environment in Debian in Tasksel
You get Gnome by default
Of course that doesn’t mean that Gnome has a better support in Debian from other Desktops (KDE, XFCE etc), but it is more likely that users will install the default; in any case this is just a small detail.
At some point Xfce  was the default desktop environment to install when the desktop task was selected, and that happened because Gnome couldn’t fit in a CD according to commit reporting from Joey.
Switch Default Desktop Task to Xfce
This ensures that the desktop will fit on CD#1, which gnome currently does not.
There may be other reasons to prefer xfce as the default as well, but that is a complex and subjective topic. Unfortunatly, Debian does not have a well-defined procedure for making such choices, though it certianly has well-defined procedures for reviewing them.
So, I’ve decided to be bold, and continue the tradition of making an arbitrary desktop selection for Debian in tasksel.
In Wheezy Beta 3 a highlight is that most of GNOME fits into CD#1 again (network-less installation).
 Noticing that Debian switch to Xfce was changed in the git but it wasn’t actually released in a stable release and Xfce default wasn’t vetted by Debian release managers. You can read more in Jeremy’s G+ about that. However there was a wrong speculation that Debian might switch to Xfce. That change is now reverted anyways.