As much as it is a sport, it still has to make money. Whereas you and I will watch every fight put on for us. Those not as interested are more likely to buy a PPV or watch a free fight if they hear its two 6'4 beasts going at it, rather than two 6 ft guys.
I get your point. Do the casual fans really think like that though? I mean, yeah you seem to be spot on in regards to why they do it, I just think that a would a one inch difference in height really affect PPV buy rates that much? If history has proven me wrong then fair play. Its just not something that has ever bothered me. If I was a casual, I'd want to see the best of the best, regardless of their stats.