They should add a contest to break it. Cause that sounds like the only real thing they can do is track the movement of the mouse / keyboard, and that sounds quite simple to fake.
Google is betting that they can extract meaning from web pages better than bots, and they have had a lot of experience with that. On Web pages, each link does not have the same probability of being clicked by a human given the list of pages seen before. Knowing that probability requires the bot to understand what a human would see, and to perform actions that match a given goal which corresponds to the sequence of pages browsed.
And that goal mustn't always be the bot's goal. Bots have business incentives: they want to get people to do something by writing text that will be seen by humans. Humans, on the other hand, only do so once in a while.