I don't really know why, other than Swamp Rat was revamped and the Rat Trap was part of that original line, or at least that's the way I think of it. I have unsubstantiated theories, but I'm sure Eric can give us an official answer.
To me, S30V is a great choice for this type of knife. Improper heat treatments can leave any steel too hard or too soft, but I've never heard of any cases like this with Rat Traps. I've carried mine daily for 2 1/2 years with no problems.
S30V is one of those steels that is to be used for cutting. Many times people will try to chop, pry or do something else that it wasn't made for. That's usually when the bad things happen.