Actually right now it's about 20% (55 out of 266 million). The high centralization of the stake is not news (it was worse a year ago), however it's unlikely that we can find an example of a coin that doesn't follow a Pareto or similar distribution of wealth (every coin has whales) it's just easier to spot in the Steem world because of the public nature of the interactions and the human readable addresses.
Note: the 20% refers to the steemit account.