There seems to be a distinct difference in how certain things can hurt you on the island:
-- There is a difference between an injury and a disease. You can't get cancer on the island, or you heal from it very quickly. (Except Ben.)
-- If you are injured, you have to treat it the same way you'd treat it anywhere else. Deadly is still deadly, etc. etc. The ONLY difference with injuries seems to be the SPEED with which they heal, not deadly they are. Something that could kill ya at home can kill ya here.
But if it doesn't kill ya, you'll heal faster. Probably a similar reason why the sperm counts are five times higher: The body makes the sperm at amazingly fast rates on the island.
It's timing, not degree.