You know, I'm curious... is there another defender class that can stop movement with their defender mechanics like the fighter can? I think this might be part of the reason for the "bodyguard" feel some people experience with the fighter.
Not all Fighters stop movement with their mechanics either, though most do. There are a number of different Defender Mechanics to allow variation in the way characters are played. Some let a monster move but then are in the monster's face whan they do move, good luck trying to stay away from an Assualt Swordmage or a Battlemind who wants to be adjacent. And try getting to a Shielding Swordmage who's taking a nerf bat to your damage numbers while engaged with someone accross the battlefield.
Heck, the actual Bodyguard-type stuff is from themes (Guardian) or there are a few powers you can choose but aren't in any way mandatory but there if you want to play that type of character.