Thing is though, in photoshop you aren't constrained by a single window for images either. In CS6 at least, images are at first tabbed but you can tear off a tab like you can in a browser, and the image will appear in a standalone window, not constrained to the main photoshop window at all. So it seems like you're in agreement with the photoshop developers anyway.
But both GIMP and Photoshop provide a single-window mode should people want it. All I use a bitmap editor for is for making the occasional avatar, messing about with photos and fairly often for taking a high-res image and cropping/adjusting/resizing it for a suitable desktop wallpaper. You can call me a noob if you like, but noobs like me are widespread and for US at least, it helps to keep things simple with a single window. But like I said, the option is still there.
Maybe you were just worried that UI development seems to be heading away from power users like yourself, and I understand. It's my pet peeve with desktop UIs nowadays, particularly in Linux. So long as options exist for everyone though, I think they should be embraced, particularly if it means more people can use computers to do something creative for a change without things being more difficult than they have to be.