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I should have said they are. There is more than look in "Look & Feel". But talking of look, Inkscape uses many GNOME icons and GIMP uses GNOME's button order. Other than widgets, GIMP doesn't look like any other Win32 app. That said, it doesn't look like any other GTK or QT app...
If you stop your comparison at screenshots, then you can conclude they look similar. But use the applications for a while and it's clear that they don't feel at home under Win32. WIMP cannot help this.