To wit, most 4e players have played a game where fighters did not have defender powers and been pretty happy with that game; it's hard to justify changing these kinds of things.
I played 3e from the time it came out until 4e did. However, I was always unsatisfied with the fighter's lack of ability to defend his party (even before 3e). We even devised various hacks, such as a Taunt skill, but they always felt klunky because earlier editions weren't designed with that sort of mechanic in mind, therefore the DM tended to make it weak in order to avoid giving the players too much "extra". Once the Knight (who had an aggro mechanic, albeit one much more primitive than marking) was released in the PHB2, I never played a fighter again. So chalk me up as someone who much prefers the 4e fighter's way of doing things, and doesn't want to go back to the pre-4 approach.
Would if make any difference if the term mark was replaced with the term threatening? Because that's typically how it's described with the fighter. The fighter threatens the target, preventing that target from fully focusing his attention on anyone else (because it's unwise to turn your back on the big man with the big sword).
I think marking is a good mechanic in a turn based game. Sure, it would be nice if the fighter could interpose himself in real time, but I've never found an elegant solution despite trying. Marking is a simplification, akin to D&D's traditional use of AC instead of DR for armor. After all, in a real fight, you can't just stroll around your opponent like you can in D&D.
Also, I'll echo those who say that there's a distinction between how defenders function and the OP's statement. Defenders protect their allies by penalizing enemies. If it worked the way the OP says it does, the fighter would give enemies a damage bonus against him, in order to give them an incentive for attacking him. That quite simply isn't how it works. After all, if only the results mattered (that the fighter is attacked instead of his allies), then most of the complaints about the 4e power system would also have to be moot, wouldn't they? You can't have it both ways...
Caramon and Raistlin (Dragonlance). Moiraine and her warder Lan (Wheel of Time). Arya Stark's defense of Mycah from Prince Joffrey (Song of Fire and Ice). The idealized form of the medieval knight. The noble warrior who interposes himself between his (or her) charge and those who would do them harm is a deeply rooted fantasy archetype. Certainly not every fighter needs a mark-like ability, but I think the designers would be remiss to exclude the mechanics to do so for those who desire to play such a character.