In the video he mentioned that he read somewhere that Block.one could not sell their 10% on the market. Not only that but they cannot even be transferred on the Ethereum network :

"The EOS Token distribution smart contract does not permit block.one to trade or transfer the Founders Tokens during the EOS Token distribution period."
Furthermore,
"block.one will lock new founders tokens distributed pursuant to such EOS Platform in a smart contract and release 10,000,000 (10%) of such tokens to block.one at the end of each one year anniversary of the genesis block over a period of 10 years."
Source: https://eos.io/faq.html

This is certainly good from an investor standpoint. Seems that for developers, it means that they will have to pay the higher price to buy/rent space on the EOS network.