If this was a conventional business, Microsoft for example, I would probably agree that more cooperation and tech sharing between the Xbox and Live divisions would be a good thing. Increase communication, reduce redundancies, all that good business stuff.
For some open source projects, like Gnome, I get the feeling the shaman is often strong than the salesman. Corporate help aside, the personal/emotional attachment of OSS contributors drives involvement in ways a big number next to market share percentage can't. But even steadfast contributors would like to see the product used, so Gnome and others aren't off the hook completely.
Should Gnome be more cooperative with 3rd party apps? Maybe. Personally, I'm thankful for the amount of quality OSS that let's a company, like Canonical, build on the shoulders of giants and offer a system better tailored for end users. That's where the request for cooperation is more realistic.
Still...
I haven't used Linux IM clients in a while but the Pidgin debacle made me wince a little.
elaborate
The developers said, well we don't want X and we only really make Pidgin for ourselves. It's just because we were feeling nice that we released it for you guys to use in the first place, we don't owe you anything.
Seriously. I've used GNOME since 2003, but these days I spend 95% of my time in Emacs and Conkeror. I keep the panel around because the wifi widget is nice, and I use nautilus a couple of times a week for the few things that are awkward to do in a shell. But GNOME is nothing more than a starting point... a blank canvas.
Then install another piece of software rather than the Gnome-branded software.
In Linux, I can eat my cake and have it too if I really want to -- I can run Amarok but use Gnome if I want. If someone wants to spend their time developing a browser suited exactly to the philosophy of the Gnome desktop, it's your decision whether or not you want to (un)install it. The only thing that gets wasted is their time.
Most non Gnome-branded apps work fine in Gnome. If GNOME wants to duplicate existing software, it's Gnome's right to do so. It's also your right to install what you want.
In other words, go to your favorite package manager, and pick what you desire. Don't be upset that you have more options. Options are the beauty of open source.