The ball was touching the arc of the corner area so it is not technically outside. But I have seen a few this season which were clearly not touching. I too find it a bit irritating. Not sure what advantage placing the ball bearly touching the line gives? Seems like a pointless bending of the rules. It is not against the rules, but is just another example of cheating, unsporting and ungentlemanly conduct.
As with any semi cheating (diving, time wasting etc) it would only take a couple of whistles and fouls called to stamp it out.
I don't think Gerards corner was foul play, but it was bordering on it. And it is endemic in he Premiership, not just Liverpool.