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OK, I think this is what I have been talking about, though maybe a case of Chinese Whispers? I have heard the 80% mined 40% given to Steem and so on, quite a few times now; anyway here it is..

Steemit, Inc mined about 60% of the available STEEM the first day and then continued to mine until it had mined over 80% of all available STEEM the first week. This representes over 320,000 STEEM mined by Steemit, Inc. Steemit then transferred 53,000 STEEM to 6 founders as VESTS. VESTS is STEEM that has been locked up for an average of 1 year, it can only be converted back to STEEM via 104 equal weekly payments. Steemit then converted its remaining STEEM into VESTS. One week after launch less than 20% of STEEM (80,0000 STEEM) was liquid and almost all of it held by anonymous miners.

Cg

I think it basically means, while steem mining was open to other miners (Because it was open to other miners, it was not a pre-mine), Steemit, Inc mined 80% of the total steem mined in the first week. Which after that was distrubuted to the founders as Steem power. Steemit, inc then powered up almost all its steem. There was 20% remaining STEEM (liquid), which was mostly held by independant miners who mined in said first week.