Adding features is important. Especially considering that GNOME 2 was missing a gigantic freaking swath of necessary features to make it actually bearable to use for anyone who wasn't weened on a terminal. Compared to an OS like Windows 7, GNOME 2 is utter crap. The problem is not the desire to improve and evolve the desktop, but the fact that the GNOME people didn't _evolve_ the deesktop -- they rewrote it half from scratch, redesigned it entirely from scratch, etc. If you want "mature" with no new features and no improvements ever, you might as well load up twm and quit bitching about DE's at all.
GNOME 3 needed to exist. It just needed to exist as GNOME 2 + Lots of Improvements, rather than to exist as iOS + WTF.