The article says that Valve is only going to make the game a Daily Deal for a single day. The polygon commenters have it right, why not make it a week?
Why not buy 138,000 copies, one for each user that wishlisted the game, and give those out gratis? At $15 per copy, that's only 2 million dollars. That's a pittance for a company the size of Valve. But that would give the devs money and time to improve the game post-launch, something they probably won't be able to do even if they take Valve's offer.