Actually I was the first to bring up every game is an RPG :P. There might be a few instances in which you can find situations when you aren’t any particular role, but you can even make up a role for yourself in those situations! In Bejeweled, you play the role of a cursor trying to swap around jewels until they match!
Anyways, I wasn’t trying to take sides, but instead just show how there is almost no set definition of what a game is or isn’t. They just are, like you say, what the developers or fanbase makes them out to be. Even technical aspects of things may contradict themselves if you keep going deeper.
Guild Wars (1) is map-based, and has a limit to the amount of players in one channel at any given time. And when you leave town to go into the field, you are actually taken to your own personal instance of the field (only you and your current party members appear in your instance). I consider it an MMO because there are various amounts of players that you can add to a friend list or guild, and chat with them no matter what map they’re in. If I really think about it, the main feature of an for me MMO is the in-game messaging system. Without that, I don’t think I would call it an MMO no matter how many people are running around the screen xD.