Joss Whedon doesn't give any credit at all to Zak Penn. The alleged classiness in personal affairs is not so obvious to eyes unblinded by $$$.
Given that the internet claque is very likely responsible for Whedon's prominence, it is not noble condescension to stroke his fans. It's his long-standing business practice, his way of publicizing himself.
As for attitude being a justification for success, personally I wish his attitude included writing things that made sense, if only in their own terms.