Maybe so. We do have some indications of possible rules.
1. I believe that there was a preview somewhere that mentioned fighters getting 2 OAs. If that's true then it's a little bit more risky to step away from him--assuming that you can't just shift and charge (which will often but not always be possible depending upon how you are based).
2. We were told that the fighter and the paladin killed the knight and took his stuff. One of the most significant knight abilities was to make every square he threatened difficult terrain. If that rule was ported into 4th edition as a fighter ability, it would make no difference to the kind of charges and movement that avoid OAs but would make it harder to move
past the warrior.
3. The newly previewed death knight miniature has a champion ability that deals damage to an adjacent enemy and prevents it from moving. If there is an action point type mechanic that emulates that, it would make fighters "sticky" but again would only help if the fighter actually bases the monster. (If you don't stick tape to something, the sticky doesn't help). It should be noted that the mini is based on a creature expected to show up at paragon levels.
4. The merchant guard mini has a bodyguard ability that lets him take an attack for an adjacent mini. We've had bodyguard effects in DDM for years without a corresponding mechanic in D&D though (yes, I know 3.0 had a devoted defender prestige class but none of the minis were based on it and their abilities worked very differently), so this might or might not reflect D&D mechanics.
5. The eternal blade has a "defender" ability that enables them to make an attack against any adjacent enemy who attacks one of their allies. (On the DDM boards, this ability has been widely decried for quite a few broken applications--particularly the way it intersects with the bodyguard ability (or at least the way it did intersect with the bodyguard ability before the draft attack resolution sequence made its way to the boards)).
6. IIRC the paladin smite preview included a smite that gave an ally a boost to AC or defenses.
7. And this is more of a disincentive to the extreme mobility afforded by charging (which is also exacerbated by the 1/1/1 rule)-- in the DDM rules, a charging creature is limited to a basic attack but a lot of creatures have more dangerous special attacks. Killing Blow--a power now seen on two fighter minis that seems to allow extra damage against bloodied targets (possibly with an attack bonus) can't be used on a charge but can be used as an attack action. Likewise, the Ossyluth's reaping claws ability more than doubles its damage output but only works as an attack action rather than a charge. More effective non-basic attacks can work as a disincentive to the move+charge mechanism to attack anyone you want any time you want and the shift+charge mechanism to escape being based and still attack anyone you want. Still, that's only a sidelight to the 1/1/1 issue (which enables more movement without charging as well as enabling far more movement than one might think while charging).
All of the abilities that I've seen in the previews or might extrapolate from the minis rules and vague preview comments (killed the knight and took his stuff) seem geared towards protecting an ally by making it unpleasant or pointless for an adjacent enemy to move away at full speed or attack anyone except you. If there are any abilities to shift when it is not your turn or immediately move to block a monster's movement, they haven't given those without playtest priviledges a hint regarding them. Perhaps more importantly, as the 3.0 Devoted Defender and the DDM bodyguard/defender combo illustrate, those abilities have at least as many offensive uses as defensive ones and possibly work even better as offensive force multipliers when applied to other so-called defenders (or maybe strikers) than when applied to those who need protection.
Mourn said:
With all this talk of fighters being "sticky," hampering the movement of foes around them, being masters of opportunity attacks and generally filling the role of "guy taking punches so you don't have to," I think it's a pretty big assumption that he can't block movement to his squishy allies.