So he's pocketing only 56,315 BTC net for 80m shares, or 0.00070394 BTC per share.
You got that wrong. Erik gets 126,315 BTC.
If I remember right, 3 more slice of 1 million shares were sold by the private investors, so 13m * 0.0035 = 45,500 BTC for MPEx holders.
It leaves 80,815 BTC to be split among the remaining 87m shares, thus 0.00092890 BTC per share. This cut is taken by Erik/private investors. Only MPEx holders are compensated at ~IPO prices. If the sale prices he quotes is true, he's giving MPEx holders almost 3x what he had to as per contract for the sale. About half the market price. It's a cut, but there wasn't enough demand to fill 87 million shares.
(By the way, for the others, even if it was not profit shares but these had voting rights, MPEx holders wouldn't be able to vote against it and the minimum compensation is indeed much lower than sale price, so he could have paid 0.00126 per share)
(a)The representatives of SatoshiDice have elected to divide SatoshiDice into 100`000`000 (one hundred million) equal non-voting shares with a total equity value of 10`000 BTC (0.0001 BTC each). In the event of liquidation or breach of this Agreement they solemnly promise and warrant to repay all investors holding shares at this minimum value.
I think this payout structure makes it even more likely that MPEx is the buyer.