Earlier quoted context omitted.
Yes. I used GIMP exclusively between 1999 and about 2009. There was always something coming in the next version that would fix GIMP. Color profiling, single window, better text tools, etc. They never did. GIMP doesn't even bother subscribing to GNOME's HIG. It's cast adrift in the world of Linux, and after a decade of using it I'm now happily on Pixelmator on OS X.
As far as I know (and I've lurking on the gimp developer list for 10+ years), GIMP has never been a GNOME application. So, from that point of view, there's no particular reason to expect it to conform to GNOME's human-interface guidelines, is there?
How about 'not being weird?' Asides from the already mentioned historic background, GNOME is the most popular OSS Unix desktop.