Exactly! Rage is an ability that the barbarian has, it's meant to be an advantage. He doesn't loose any int or wis while raging, nor is it stated anywhere that he looses any amount of control over himself. If that were the case I'd never even rage as a barbarian (or rarely), or just play a fighter all along. What the fighter does with technique (=feats) the barbarian does with mere power (rage) and instinct (uncanny dodge). He is still a skilled fighter after all...
edit: Let's approach it from a rules point of view. If it were meant to be limiting to the way he can act, it would be listed in the description of rage. He does become "more reckless and less able to defend himself", as represented by the -2 to AC. He can't use any charisma, dexteity or intelligence based skills with the exceptions listed. No spellcasting, concentrating, using any magic items or using combat expertise. Now it is also stated that he "can't use any abilities that require patience or concentration". That's the point where it's up to the GM to decide if a) readying an action is an ability (only a technicality if you ask me) and b) if it's actually already in the definition of beeing patient to wait for someone to charge if you expect him to (for example since he's holding a lance and riding a horse, which usually is a pretty good clue). I would not let him ready the action for 2 or more rounds in a row so that he just keeps waiting, but once: no problem there! If you diallow it, you would also have to deny him a refocus and wait (which both are intentionally waiting, beeing patient in the same ways that the ready action is).