I agree at one level, and disagree at another. As a player, its really cool to pull off those excellent reaction powers associated with the mark, its can make playing the tank fun. Yet the role of the tank is to draw fire away from the reast of the team, and the "artificial" interpretation suits that better.This is the same argument I have with my DM regarding marks. My wife plays a Warden. She marks everything she can get near, and she never gets to use any of her At-Will "you didn't attack me" powers because the DM insists that the monsters know what she's capable of doing to them as soon as they're marked.
I say (and I've ruled in my own game) that the monster knows it's marked (and knows it takes a -2 to hit anyone but the marking creature) but it doesn't know what that creature's abilities are in regards to an ignored mark, unless the ramifications for ignoring said mark are part of the marking power (like a swordmage or paladin). Fighters and Wardens have special class abilities that kick in if a mark is ignored, but it's not a condition of the mark itself.
If only my DM would see it that way, I'd stop having to bite my tongue, and my wife wouldn't feel like so many of her class features are getting completely ignored. =/
As a DM I rule both ways. If the party is really in a pinch (i.e. things are looking rough) I play the "creature is marked, creature knows and therefore goes for tank" approach, otherwise (which is more often) I will play the "creature doesnt know" approach so the players can enjoy the playing experience a bit more.
Mind you, I dont tell the players thats my approach, and no-one has really guessed. They just know sometimes I rule one way and the rest I rule the other. Keeps em on their toes.