Hunt by the time he got to UFC was so battle worn it's not even funny.
Hunt took damage from Lebanner X 3, Hoost, Sefo(All out war), Prime Wanderlei, Crocop X2
by the time Manhoef knocked Hunt out, he was already out of his prime.
By the time he got to the UFC, he was wayyyyyyyyyyyyyyyyy past prime. This should actually speak to the longevity of his chin. Most people become glass jawed after they've been KOed a couple times.