I've done a little bare knuckle boxing before. Lots of people injure their hands doing it. Google a picture of Lenny McLean's hands, most people's hands start looking like that pretty quickly, like within a year or two.
As for people not getting injured, well everyone has some different attributes etc. I have always been considered a liar when I say it, and then a freak of nature when I'd prove it, but I have for a long, long time been comfortable and able to pound on the heavy bag as hard as I can for round after round of bag work without gloves or wraps and not injure my hands or wrists - although now I am getting a little older my elbows start to get twingey if I don't warm up properly first. And I weight 245lbs so I'm not pitter-patting on the bag, it's big booming shovel hooks that send it flying, big straight lefts and what have you. That's just part of my natural attributes - but on the flipside my wrists are really inflexible and tight most of the time and my hands are misshapen scarred and ugly. I started working in bareknuckle bag work about 15 or 16 years ago as a way of checking for correct form/technique which an old school boxing coach clued me into, but then I started getting comfortable that way and ended up preferring it.
I've had boxer's fractures a bunch of times back when I was fighting MT, every time I got it was in the gloves.
M.O.B.F.O.E. - Money Over Bitches, Fitness Over Everything