meta-gnome3 is Debian's source for GNOME metapackages similar to our ubuntu-meta. Some users use these as a base to use Ubuntu without Unity, so including this is a high priority for those users.
meta-gnome2 was removed (bug 828537) because Ubuntu doesn't ship GNOME 2 any more. Debian just made its first release of meta-gnome3 in experimental yesterday so it wasn't possible to add this earlier.
meta-gnome3 is Debian's source for GNOME metapackages similar to our ubuntu-meta. Some users use these as a base to use Ubuntu without Unity, so including this is a high priority for those users.
meta-gnome2 was removed (bug 828537) because Ubuntu doesn't ship GNOME 2 any more. Debian just made its first release of meta-gnome3 in experimental yesterday so it wasn't possible to add this earlier.