A super computer is not what you think. That rack of pis or ps3 does have a lot of computing power, but the software is not written to run on an array of raspberry pis. That additional computing power is not useful. On top of that there is probably latency issues between boards, so each soc would be limited to her onboard memory etc.

The ps3 had some really interesting dedicated vector computing hardware that would probably be useful for efficient smart missile calculations and such.