JohnSnow
Hero
I personally think that humans can choose the racial power in place of a third at-will attack power. It will solve the problems of humans belonging to a class with no at-will attack powers quite neatly.
My theory is that the bonus at-will has been left intact (fighters just get an extra stance and thieves an extra trick), and that this power is entirely additive. I'm guessing it's acquired via a feat somewhat similar to the bloodline feats that have been presented in past articles in Dragon.