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.
