I agree. Also, the big names are making their fair share of dough. Both Hughes and Gracie made more than a million each off of UFC 60's purses and ppv shares, not to mention whatever they got for sponsorships, etc. Granted that was a marquee fight and both are big names but I just don't think that the money criticism flies when you consider what a significant portion of the fighters make.
Also, they will make more money as the sport grows. No doubt early football players knocked the crap out of each other too and made no money for it, but that was because no one cared. As soon as MMA collects a large audience that cares, the money will follow suit.