This is not the reason. Monte Carlo programs typically play bad-looking moves in way ahead / way behind situations. In these situations "bad" moves will sometim

This is not the reason. Monte Carlo programs typically play bad-looking moves in way ahead / way behind situations. In these situations "bad" moves will sometimes not alter the win probability they measure, so they don't know how to disguinish a more natural move from one that looks bad. This was mentioned in the commentary when one of the DeepMind guys came in. Go programmers have taken various steps to mitigate this behavior, such as dynamically adjusting komi to trick the engine into thinking it is a closer game, but I don't know if AlphaGo uses any such technique.