Awful thread about 5ft steps
I agree.
Except both readied actions and AoO's clearly state they happen BEFORE the triggering action.No, the rules clearly state that both of those actions resolve before the triggering action. If the triggering action doesn't happen then the AoO or Readied Action couldn't trigger. Imagine a fight where your opponent tries to disarm you. He strikes at your sword arm, attempting to knock your weapon from your hand but leaves himself vulnerable (no special training to disarm; i.e. no Imp Disarm feat). You quickly strike at him, attempting to kill him before he can knock your weapon away. Whether you succeed or not, he has still extended himself in that way to allow himself to become open to attack. The thought of disarming you is not what left him open, the attempt did.
Readying an Action: The action occurs just before the action that triggers it.
The entire reason that a trip lock is not valid is because the trip attempt happens BEFORE a person can stand up and does not interrupt them standing up. If it started after they began standing, you could keep them on the ground.