A redirection of mapquest.com to mapquest.aol might help with branding, while music.aol is their current product. They don’t appear to own music.com, so unless they were going to license aol as a subdomain from a third party, they might want to stick with what they have and instead of AOL[dot], turn their marketing around to [dot]AOL.

/2 cents

I’d guess that very few people know that Mapquest is an aol property, so it’s an established brand and they might want to put the aol in front for marketing and well, music.com doesn’t appear to be an aol property, while music.aol will come up in a search.