I have a feeling they are not selling, if they where selling the price would be diving down to new lows as they hold over 10% of all the steem. Instead its doing to opposite. If they do sell off I think its going to be a flash crash and not what we are seeing right now.

But yes steemit should sell to cover costs but should also contribute some how to the price of steem by running ads etc. From what I recall steemit takes 25% of every upvote