Looking at tasksel’s changelog on a Sid installation, I see the last change was v3.12 from 21 July 2012 and I cannot find anything about changing the default desktop environment for the desktop task. So, maybe this change is not meant for the frozen Wheezy, whose taskel is already behind Sid’s (v3.11 compared to Sid’s v3.12).

Maybe someone familiar with Debian’s decision-making and development processes could enligthen us.