Kutcher is definitely not wearing a piece. But, something awesome happened to his hair. Check out his movie Spread. His hair is awesome in that movie.
Made me so envious. And there are several shots with his hair pulled back and with him swimming as well.
I remember seeing some sort of gossip tidbit years ago about Kutcher being panicked about his hair loss and had been using Rogaine. I don't know if he had a hair transplant or not but I think it's possible that he may have started using minoxidil and finasteride and had his hair loss stabilize while hiding the recession with different hairstyles.
The pic of him in the pool for the Spread poster is most likely just photoshopped. Does he show off his hairline in the movie? If I'm wrong then I suppose he could have had a hair transplant. It wouldn't be too hard to bring him from where he was to a Norwood 1.5 or 2.
I remember he was on Jay Leno about a year ago, maybe less and he played a game with a ball or something, then they dropped a load of water on him and he pulled his hair back and his hairline was pretty much straight and he was soaked.
He does show it off in the movie. In the pool they show a close up of him coming out of the water and swiping his hair back. Looks 100% natural.
Also there are a few times where they show him with his hair combed back and looks awesome. DAMN HIM!!!!!