The pay will go up in time. And the guys who are the most exciting are getting paid well. The guys that aren't, it's cuz they aren't exciting! Or it's cuz they are too new.
Look at GSP, you watch in the next two years his purses will double at least.
Hughes got big money, you all like Hughes. Liddell is well paid, Ortiz, etc. Monson got the short end of the stick but I didn't hear anybody talking about Monson being their favorite fighter or wanting to watch him fight 4 times a year. It's all about the draw.
Now if they paid someone you LOVE to watch crap, then that's a different story. But I don't see that happening really. Even my guy Nick Diaz got 24k on an undercard that wasn't shown. Fair enough to me.
As the venues get bigger (Pride has way bigger shows) and the UFC continues to grow, the pay will go up. In the meantime, if any of the fighters had a problem with how they get paid, you'd hear about it. And you don't. Not since Ortiz complained his ass off and went to go wrestle.