Erik Morales was only stopped twice, both times to pacquiao & neither of those times were down to his chin.
Castillo was weird chin wise. You'd think it was iron looking at certain fights, but then you dig and see that he was stopped by Cesar Soto, and that was certainly no cuts stoppage. It was actually eerily similar to his knockout loss to Corales, pinned against the ropes being hit by flush shots, head lashing around... but not going down. :think
Surprised no one has mentioned Holyfield in Bowe III Katsidis has been stopped a few times as well purely because he blocks punches with his head. Margarito and Mayorga were both stopped by Cotto and Mosley (De La Hoya and Tito aswell for Mayorga) De La Hoya Vs B-hop and PAC.
He was also badly hurt by Cesar Bazan but he kept his cool and ended up stopping Bazan a couple of rounds later.