User blog comment:Dryst97/Fire is Superior than magma/@comment-835210-20100215032729

Possibly Akainu has some mastery of an outside source of power, such as Haki, that was stronger than Ace's. Either way, I think Ace had no choice but to stay solid to prevent that attack from hitting Luffy. If he had dissipated, the punch would have killed the already weakened Luffy. :/