I think it's worth noting that MMA fighters don't tend to suffer as many injuries. Boxing's strict ruleset forces fighters to beat eachother into putty to win, but other fights can be won without (as many) concussions.
The difference in MMA is that as soon as a fighter is not intelligently defending themselves, the ref stops the fight. There is a much lower standard for a technical knockout. There are many stoppages that occur after "flash" knockouts, where the fighter is only unconscious for a brief moment. Usually the fighter will protest, as he doesn't even realize it's happened. In boxing, a flash knockout doesn't end the fight, as long as the fighter gets back up. In a boxing match, this could happen twice every round without ending the fight.
I also wonder if the ability to wrestle in MMA plays a role. In boxing, as soon as the fighters clinch, the ref breaks up the fighters. In MMA, it's rare to see fighters stand within each other's range and throw full powered punches for extended periods.
Is there concrete data to back that up? There have been terrible bone breaks and joint damage in mma. It also seems too young to know if there will be the same neurological issues. It could be true but it also sounds like marketing.
I also wonder if the ability to wrestle in MMA plays a role. In boxing, as soon as the fighters clinch, the ref breaks up the fighters. In MMA, it's rare to see fighters stand within each other's range and throw full powered punches for extended periods.