IMO that section simply states how to determine if an enemy grants cover against ranged attacks, as stated in the previous section that strongly seems to imply that enemies only grant cover against ranged attacks.
Normal cover also protects against melee attacks, so it is clear that enemies don't provide "standard" cover.
I agree with this point. My logic is thus:
“Creatures and Cover: When you make a ranged attack against an enemy and other enemies are in the way, your target has cover. Your allies never grant cover to your enemies, and neither allies nor enemies give cover against melee, close, or area attacks.”
We know that allies never grant cover to your enemies, so we can assume that it’s not the fact that there’s a creature in the square that’s granting the cover … it’s something to do with the creature’s allegiance and intent. So a body standing there doesn’t actually grant cover, in and of itself.
Now notice that the rules only stipulate that your target has cover
when you make a ranged attack. So it’s as if you, as the target, suddenly have a split second of cover and could make a stealth check … if only you were taking an action. But you’re not, so it’s moot for the purposes of combat advantage or hiding from view. As soon as the ranged attack is complete, your cover is also gone, and so is your opportunity to make a stealth check. Even rogue powers like chameleon and hide in plain sight don't let you piggyback into suddenly disappearing (but only after a guy lobs something at you), because they only let you stay hidden if you were
already hidden, and until the moment of the ranged attack, you didn't have cover to try to hide behind.
Another way of looking at it is that the ally, as a free action possible only when you’re being attacked by a ranged attack, is choosing to give you cover against that precise attack.
I think that interpretation holds up pretty well in relation to the other game mechanics, doesn't hinder rogues overly much, and doesn't strain believability. Plus, there's a loophole: if a rogue has a way to make a stealth check as an interrupt, or even a stealth check and an attack as an interrupt, they could absolutely get combat advantage for that interrupting attack … they deserve it, after all of that effort!