Ah, the Minimum Resale Price Restriction loophole, also known as vertical price fixing. Y'know, I'm sure a lot of companies were quite happy when this practice was declared legal by the Supreme Court. However, these agreements only tell retailers what the minimum price they can resell merchandise at. It's not the same as a retailer being told exactly how much they have to sell a product for.
What would be truly illegal would be if competing manufacturers got together to artificially set prices at certain levels, free-market be damned. That would be horizontal price fixing and it's still pounced on by the Justice Department. (e.g.: airlines colluding to set jet fuel surcharge prices)
That being said, I will admit that the tone of my first post was pretty strong and black-and-white. I should have qualified it better. Sorry 'bout that. But shades-of-grey aside, I still stand by the basic gist of what I said.
Yes MAP and lots of companies do it and usually the only ones that don't sell for lower are the big guys like GC. However in the case of Mesa they completely enforce it. They can't legally drop the seller for selling lower but what they do is not honor the warranty for the customer. So if you buy a Mesa at lower than MAP you bought it without a warranty.