Could this be a sign of the Nats trying to force some re-negotiation/re-assignment of territory or perhaps influence the next round of the endless MASN dispute? The Nats are not new to the world of corporate contracts and would have known even before planning last year's game that they're not allowed to play there, based on how the territories are drawn up. While contractually the Nats would be clearly in the wrong, in the court of public opinion, Angelos is the bad guy, and now the Nats can say "look at all these letters/emails/posts, clearly the Nats fans in Annapolis outnumber the O's fans." Angelos could avoid this by either allowing the Nats to play there, having the O's take over the series, or, even better, insisting that it's a Nats-O's matchup, but he's either too stupid or too petty to do that.
Or maybe my tinfoil hat is too tight.