In the comics, Blob's head is supposed to be more vulnerable than the rest of his fat-covered body. I assumed that was what they were sticking with when Logan KO'ed him with head shots. Yes, I'm sure he is still fairly durable and it took adamantium to allow a KO. He is also shown as being very tall and his head would be kinda hard to reach for a shorter boxer.
Each one of his hits would KO either Rocky or Daredevil. He knocked Wolverine far out of the ring.