It is only a matter of time. Sure, Japan currently has a much bigger fan base and Pride firmly has the the competitive advantage in that important respect. However, I has been my obversation that American Boxing fans (in DROVES) are transferring interest to MMA. American Boxing fan numbers are LARGE, especially among Latinos, who currently make up around ~45 million Americans.
Eventually, the UFC will be offering much bigger paydays than their Japanese counterpart and all the talent will be here.
Sure, they are being a little greedy and shorting fighers right now, but that won't last long.
In five years, the U.S. will be the center of MMA!