I believe this was brought up in the Telegram channel a couple of times. Founders / block.one have promised not to buy EOS tokens during the ICO. However, they are free to take ETH and do with them what they want (other than buying EOS tokens).

See relevant parts of the EOS FAQ:

"The EOS Token distribution smart contract does not permit block.one to trade or transfer the Founders Tokens during the EOS Token distribution period."

"As a private company, proceeds of the EOS Token distribution will be utilized by block.one in its sole discretion"

"26. Will block.one be contributing to the EOS Token distribution?
No, during the entire EOS Token distribution period, block.one will not do any of the following:
block.one will not purchase EOS Tokens by any means;
block.one will not pay any dividends to its shareholders; and
block.one will not perform any share buybacks.
block.one intends to engage an independent third party auditor who will release an independent audit report providing further assurances that block.one has not purchased EOS Tokens during the EOS Token distribution period or traded EOS Tokens (including using proceeds from the EOS Token distribution for these purposes). This report will be made available to the public on the eos.io website"

I do not worry about this. For those that worry, why run the risk of ruining reputation right now if the mother load was already received by block.one in round 0?