Well, it's almost equally impressive that he didn't lose a lot of his gains. He took advantage of the upside and avoided a lot of the downside in the markets. If you think it's impossible to beat the market over long periods of time, shouldn't his returns averaged out to normal or worse than the market average after 20 years?
You can obviously beat the market if you are really smart or lucky or both. I agree though that very few do and many try to beat it and end up under performing the market.
No, there is no obviously beating the market because you're really smart. The only guy you have found so far is some guy who made a non-detailed blog comment about his 20 year investment where he didn't beat the market for nearly half the time. If you get lucky, you can be profitable in the short term, just like gambling. There is no stock investment strategy that beats the market over the long term other than insider trading.