I have figured out the meaning behind the super only kills. It actually makes sense, it actually has a meaning. Here it is:
These are All-Stars, not your ordinary average joes. It will take more then a good beating to kill them. Sly Cooper can't run up and beat the crud out of Kratos and kill him. Kratos is too strong, therefore it will require Slys best to defeat him, which is what a super is, the best of the best. These are Heros! Unlike in smash where if Mario fell of a cliff it would kill him, in this game our Heros don't die by falling off cliffs, no, these All-Stars are made of tougher things! They re-spawn at the top, not with death, but a small penalty! Supers are the best of the best, which is why the supers make sense. It takes the best, to kill the best.