The way I read that comment suggests that the attacker overextends his balance because he expects to hit the target. Is that what you mean?
I mean that every target presents some kind of resistance, be it a wooden door or a human body or a pile of bricks. I believe the amount of power put in a strike is proportional to the amount of resistance the attacker expects to receive. When the encountered resistance is nil, there must be some kind of loss of balance even by the most experienced martial artists.
A Karateka can hit the air while performing a Kata with great power without loosing balance because he did not expect resistance, but the same Karateka if he's trying to break a pile of bricks will surely loose his balance if the bricks were to suddenly disappear just before the moment of impact.
But I could be wrong.