The 90%/10% split might just be an april fools day prank, but I don't think so.
The upshot of the O's having all the risk on this is that TV networks like this have failed in the past. And if this deal, as it plays out, truly looks like a stinker, then DC's fans, as the larger market, can sink the network in an instant by refusing to watch. A boycott of the network called by any of the DC sportswriters could sink the zeppelin pretty quickly, and although Angelos might try to sue every resident of the city of DC individually, I doubt that he'd get too far with that. (I'm reminded of an old Mr. Show bit about Coupon: The Movie, where a movie studio successfully sued all of America for not watching their crappy movie.)