Yep. And it would probably be good for altcoins indeed. It just can't be a good bitcoin miner because the ASICs are already out there. If an altcoin can be mined with an ASIC (I believe the purpose of some, like litecoin, are not to be?) then it is near pointless to mine with a GPU (unless in a pool).

Also, I would assume the reason behind supercomputers not being good for gaming is that they are parallelized in ways other than the chips on the GPU (entire machines are networked together via various interfaces). The software behind distributing the processing between several machines, or whatever aspect makes it super, is probably what limits the ability of supercomputers to run video games :0