Yeah, I was going to touch on that earlier, but I was going to be very long winded about it and probably contradict myself about six or seven times, so I decided against it. But here goes nothing...
I do agree with you that the casual fans want to see the biggest guys, but they also want to see the strikers; the guys that are capable of delivering a KO. That is why heavyweight boxing is struggling, because aside from Klitschko and maybe Samuel Peter, you are not really going to see a lot of excitement. And that is why a lot of fans have, and rightfully so, shifted their attention to the lower weight classes where the fights are more exciting.
I think MMA is similar, like you said. And like boxing, I think the divisions below HW have the most exciting fighters, smaller obviously, but that are still capable of ending a fight at any moment. That is why lower weight classes in boxing struggle, because featherweights can go out there and punch for days, but they do not carry any power. So most of the time it goes to the scorecards.
But in MMA, there is a lot more than one way to end a fight. You see a guy like Faber that is so fundamentally sound in so many diciplines and has so many ways to end a fight. I guess what I am saying is that the excitement, the drama is there in MMA regardless of weight class, and the smaller guys are going to have a lot better chance at recognition than they will in boxing.