In addition to what's been posted, I suspect it has a lot to do with the individual. I mean, how many guys are physically capable of doing what Lyoto does, at the level he does it in the UFC?
You would have to be able to couple a lot speed with reflexes. And not just striking speed, but movement in the octagon. Not sure how many guys can do that using primarily Karate.
And let's not forget that he uses Sumo and Judo as well.
While his stance and striking approach are undeniably Karate-centric, the other parts of his MMA recipe are equally as important to what he does.