I personally find endorsements to be a little odious. Things are much worse in the guitar world though, where certain famous guitarists seem to have a signature everything with their logo on just to make a few bucks (Slash, i'm looking at you !). I'm sure they don't use much of this stuff and have just agreed for their name to go on it as they know it's a good revenue stream.
Even though i'm no pro, I'd be reluctant to be limited to a certain brand as I think it'd limit my creativity soundwise, but I get the feeling a lot of endorsees aren't that bothered.