He should be fit for the most part like I questioned. He is mature enough that he realizes he can do other physical activities to stay in tip top shape (like running) so that when his wrist is healed, he can just concentrate on strengthening the wrist and his tennis.
Why do you have to be 100%? There are plenty of players that are not injured that do not feel 100%, but they step on the court.
You don't have to be 100% because no-one genuinely is, but this is a wrist we are dealing with. Those types of injuries are potentially chronic and will/have destroyed careers. He should be fit in terms of the legs, back etc., but he still is strengthening his wrist, it isn't 100% yet. His wrist is still weak at this point in time, making it more suspect to potential re-tears and damage. Obviously, after everything he has been through, he doesn't want to take that risk, and he shouldn't. The long term is more important that short term satisfaction, because he isn't prepared to truly be a threat at the US Open anyway. Unlike other guys, he has this major and he has lots of money so there incentive to play at 50% isn't nearly as high for him. He wants to get back to being the best of his capabilities at the top of the game and he shouldn't put any roadblocks in the way of achieving that goal.