Many distributions (Ubuntu, etc.) treat GTK as the platform's native GUI toolkit, at least in terms of customization and accessibility features. And, from what

Many distributions (Ubuntu, etc.) treat GTK as the platform's native GUI toolkit, at least in terms of customization and accessibility features. And, from what I've read on @raphlinus' blog, one of the goals is to integrate well with the native platform. So I think, rather than defeating the purpose, it's entirely in line with the purpose.