I see this from totally a user experience side. NoCAPTCHA isn't about defeating spam (you're right, the spammers are going to solve it/hire someone to finish the job etc) - it's about making a better experience for the humans, while slowing down the spammers a bit. (contrary to current recaptcha system that slows down spammers a bit or not at all, and makes life mostly more crappy for humans)