Most other distros don't have shared-mime-info as a dep of gdk-pixbuf2, and gdk-pixbuf2 functions by itself without it as a dep. But Arch linux has shared-mime-info as a dependency for gtk2, Debian has it as a dep of gtk2, gentoo has it as a depends of gtk2 when certain use flags are used. It appears gtk2 works with some packages without shared-mime-info, and we previously been adding shared-mime-info as a dep to apps that need it to function. Though it would add ~500kb worth of dependencies for simple apps like leafpad and Mplayer-gtk2 that doesn't need it, it would also be simpler and save time and build/runtime troubleshooting to add shared-mime-info as a dep of gtk2. Simplicity vs minimal deps and small size potential. I slightly lean toward issuing a statement in the gtk2 info file that many graphical apps require shared-mime-info rather than to impose it on small apps that don't need it. I will ponder it today.
If shared-mime-info is added as a dep of gdk-pixbuf2 or gtk2, I think it would make more sense for it to be a dep of gtk2, though it technically wouldn't matter as I don't know of any uses of gdk-pixbuf2 outside of it's use with gtk2.