GTK+ and Gnome are not the same
It's important to distinguish between "Gnome" and "GTK+". While there may be arguments for making Gnome "linux only" (I'd probably disagree with them -- portability can be a huge pain, but in the end almost always increases technical quality), GTK+ is different: I think it would be a huge mistake to make GTK+ linux only. Indeed, they should be trying to make GTK+ more portable.
Originally Posted by liam
App writers may typically emphasize a certain OS as a target, but being able to port to other OSes without a complete rewrite is a huge benefit; if I'm trying to choose a UI toolkit for a project, "linux only" would be a big turnoff. Even if in practice a toolkit may work better on linux," there's a stark difference between "better" and "only."
This sort of balkanization is a mistake, and will make developers more reluctant to use GTK+.
[There seems to be a worrying tendency to conflate GTK+ and Gnome, but GTK+ is (at least so far) very useful outside of Gnome, and (er... so far) comes with a lot less baggage (political and otherwise).]