Quote Originally Posted by ssam View Post

you cannot have Gnome2 and Gnome3 components installed on the same system at the same time (without a real mess). Its not hard to make Gnome2 and Gnome3 parallel installable, Mate managed just by changing the names. Just like its possible to have GTK2 and GTK3 installed at the same time, or gstreamer 0.10 and 1.0. I am fairly sure KDE3 and KDE4 could be installed together.

If the Gnome devs had bumped the names, or libraries version, or however everyone else does it, then the distros would have been free to offer GNOME3 and keep GNOME2 alongside.

whether the gnome devs made a concious effort to prevent this. or just never got around to making the parallel install work, is a difficult question.

The part you don't seem to be grasping here is that Gnome 2 is no longer supported. It would have made absolutely zero sense for the Gnome devs to go to the trouble of renaming half of Gnome 2 so that it could be installed alongside 3, when they had no intention of further developing or supporting that codebase. Did they rename things at the final release of Gnome v1 so that users could keep on running unsupported code next to Gnome v2? No, and it's not reasonable to expect that they should have done it at v3.