I think Bill Ayer's last letter that he sent to my home said it all (and I'm paraphrasing because my wife tore up the letter in fury and tossed it): AAG wants to get rid of the Horizon RJs because they're not too efficient.

Now the Q400 sure is an efficient bird, but there are some longer routes that are simply best served by a jet, and those routes may not have the traffic to support a 737. Hence: Later on in the letter, he lets slip how they might seek to contract out regional jet flying to fill the void left by Horizon's RJs. Helllloooooooo Mesa!

My two cents: It's the first shot across the bow. I don't believe Ayer's prime motivator here is fuel prices; it's Horizon RJ captain prices.