GOF, the problem isn't whether or nor the player sees it coming, but the character. A straight HP system without any mechanics for dealing with surprise as it pertains to taking damage (like D&D and others) says that they always see it coming - even when they don't, and is too abstract for me and apparently, others.
So, if the game has it D&D-like, then it really doesn't matter if the player sees his character getting attacked, as the damage he takes is the same as if he was struck from the front and knew it was coming. Their attacker will just get an extra hit in before they realize they are being attacked. In an RM rules engined MMO, getting attacked from behind/surprise would be much more dangerous, and therefore you would have to plan accordingly. Like ensure the people in your group are covering their "arcs" so no one gets caught un-awares, and to try to catch your opponents off-guard as it is a viable tactic. (Unlike in D&D, unless you are rogue or something else that gets the "special ability" to attack from surprise and have it matter.) This is why I would prefer an MMO with an engine that emulates RM style play over one like D&D.
I do agree that there is more of the player's abilities being brought into the foreground for an MMO, then for a tabletop. But, with modern programing I am sure that something can be done to help here. Like an "if, then" style, where it is: if sneaking, then use targets perception skills, and if successful then a visual or audible warning is given them. I am not a programmer (obviously), so I don't know exactly how it would/could work, but I am sure that it can be done.
