These addresses could very well be storing funds belonging to thousands of people.
Then, on the other hand, we don't know how many addresses the super-bitcoin-holders have.
We don't know the addresses belonging to the Winklevii. We already know that satoshi has around 20,000 addresses.
The chart is inconclusive at best.
Wow, I really thought that more bitcoins were lost by now. How did they even figure this out??? How do we know the Bitcoins in the addresses with most Bitcoins aren't really lost? We've really only 10 million BTC left to be mined, so we're at about 1/2 of the total amount to be ever distributed. Amazing!