>>Actually, I think that it's because gem uninstall defaults to
>>installing from the system gem directory.

>  ¨ÂÁÒÎÉÎÇ ¨Âîóôáììéîôï þ¯®çåí óéîã¯õóò¯ìéâ¯òõâù¯çåí󯱮¸ áî> usr/bin aren't both writable.

Sorry for being vague.  That's what I meant, actually.  That is, since ruby in general couldn't run the gems there as the location wasn't in the path, it wouldn't be able to uninstall them, either.