Well I don't think that Gnome has really had that hard and fast rules to what is 'Gnome' or not.
Only so much what is in the default Gnome.
Just because people almost never ship what is in the default Gnome setup. The most common modifications are to use Firefox instead of Epiphany and add on OpenOffice.org, but there are lots of other mods people do. Themes, configuration tools, default configurations of gnome applications.
And I have not seen any Gnome devs complaining about or anything. At least nothing beyond ignoring pathes for PA and breaking it with bad configurations and such, or occasional input into things like the 'Ubuntu Button Placement' drama.
That and they occasionally bring back in mods and add-ons into to the project's default installs. The biggest example is Novell's Gnome C# support and Tomboy.
That and they have support for lots of things that are not part of the default install. Like all the other language bindings besides C, Python, and C#.
So i don't think that Ubuntu is doing anything weird or unusual here. Maybe they could be working closer with upstream, or maybe not. I don't know, but the most important thing that Ubuntu can do is get it done and out there as quickly as possible so that they can get lots of feedback.