Before the Steam Summer Sale Started, on the Steam forums, people were worried that if D:OS were to be released on the last day, sales would suffer because people had already spent their money during the sale.
That's a reasonable point, and I think this day 1 sale is a very clever solution. You get the attention of the sale start, when people have peak money, and then it goes back down afterwards.
As to the argument "I paid for early access..." well yes, but Early Access is pretty much over - the game is coming out in 11 days.
