You make a valid point, although I believe that saying still has value. Perhaps not as a statement meant to "prove" anything, but it helps show that absolutes do not exist. "There is nothing God can not do" is an absolute, but it doesn't work. If there is nothing God can't do, than God cannot do "nothing". This would make more sense if I wasn't stoned.

Anyways, the problem with this is...if nothing is an absolute...isn't that an absolute? Another paradox.