The argument that AI is either much better or much worse does not apply here. It's not an accident that they chose this point in time to play against Lee Sedol instead of 10 years ago or 10 years in the future. They chose this point in time because they thought that they have a reasonable chance of winning.
Also, he won with white but he will play with black next time, so playing the same sequence of moves can't happen. Additionally, even if the AI didn't incorporate any randomness in the opening (I think it does) it may choose different moves if it gets a different amount of time to think, so Lee Sedol would have to play his moves at exactly the same time as the last game. A couple of seconds deviation only has to lead to a different move in one of the 80 or so moves before the mistake was made to invalidate this strategy.
> It's not an accident that they chose this point in time to play against Lee Sedol instead of 10 years ago or 10 years in the future. They chose this point in time because they thought that they have a reasonable chance of winning.
Most importantly, they chose this point in time because they know that there are several other AI research teams that are also on the right track (including at Facebook). Like circumnavigating the globe or landing on the Moon, 90% of the benefit of it is lost if someone else does it before you. So you don't wait for 100% certainty of winning -- you are maximizing for the chance of winning first, not winning for certain.
Given that, it seems reasonable that they would go after Lee Sedol when they were sure they were better than him, but not too much better than him. So a non-5-0 outcome is, in hindsight, not horribly surprising.
That kind of makes sense, however the point was more that AI progress isn't gradual and continuous. It's (sometimes) rapid and has discontinuities.
Alphago was an entirely new method, using deep convolutional neural networks as a move generator. Therefore there wasn't any guarantee that it had to be just slightly better than previous Go playing algorithms, it could have easily been far above humans.
Likewise this is also the first time Go AI has been given Google scale resources. Both in terms of a team of the best researchers working full time on it, and their computing power. Whereas previous Go projects were all hobbyist things.
And Google didn't wait 10 years to challenge Sedol. The match was arranged only a few months at most after they started developing it.
Also, he won with white but he will play with black next time, so playing the same sequence of moves can't happen. Additionally, even if the AI didn't incorporate any randomness in the opening (I think it does) it may choose different moves if it gets a different amount of time to think, so Lee Sedol would have to play his moves at exactly the same time as the last game. A couple of seconds deviation only has to lead to a different move in one of the 80 or so moves before the mistake was made to invalidate this strategy.