You are very correct sir. Put Kelly Pavlik fighting Paul Williams at 160 for the Middleweight Crown in Youngstown, and that is a major, local sell out. Vegas, at this point is fine for a Megafight, but horrid for a mid tier fight. Toney vs. Hopkins would sell fine at the MGM Grand, but Hopkins against Adamek would lose $$$ in the same venue.
I actually don't mind fights moving away from Vegas. The first four rows on all sides of the ring go to celebrities and whales anyway. Let's bring it back to the people!