Here's an example of an archive manager today (xfce on debian unstable): http://ugcs.caltech.edu/~ohazi/misc/file-roller-gnome.png
What it used to look like: http://repo.openpandora.org/files/pnd/fileroller/previews/fi...
This is slowly happening with a lot of applications that I use regularly.
> What is it that GNOME devs do that is so valuable and unique?
In my opinion the biggest problem is that they still control mainline GTK. Many of the high quality Linux desktop apps "automatically" fall under the GNOME umbrella because of this, and it's going to take a lot more than just switching to xfce to get them back out. It's become pretty clear to me that GNOME is trying to become a mobile first platform, and that they'd like to take many of my desktop applications with them. I'm not really sure what a good long term solution to this problem is.
Red Hat is probably the biggest sugar daddy GNOME has. They've always shipped a GNOME desktop as their default desktop in RHEL, and they employ a lot of the GNOME developers.
Xfce is, in my opinion, a better and more focused desktop, but it was "not invented there" and so doesn't get very much PR from Red Hat. Ubuntu, of course, is pushing their own crappy desktop and doesn't have any incentive to make people aware of alternatives. Most of the Xfce devs are in Europe, I think.
Arguably, what happened here is that Microsoft Windows jumped off a cliff, and GNOME and Unity said, "wow! let's do that." The idea of having the same interface on a tablet as on a desktop is an old one with Microsoft (it's why Windows CE was such a flop) but it just keeps coming up again at that company. Now I think some people are starting to see the pavement approaching at terminal velocity. Hopefully we'll get our start menus and windows back in the next year or two (from Redmond and GNOME).
http://www.omgubuntu.co.uk/2013/11/debian-8-0-switches-xfce-...
In general, most of the GNOME devs work for Red Hat. Debian is not really that closely associated with GNOME, and a lot of the Debian devs have gotten annoyed by GNOME decisions in the past. I think the latest example was when GNOME started to depend on systemd, some Debian developers were annoyed.
I haven't used a DE in a while, though. A basic composite/tiling WM is enough. Anything else is superfluous, although I do enjoy Xfce.