They are coming from Nvidia, but they aren't the ones manufacturing the 599 card. It's basically a MAP price. They haven't come out and said that, but that's kinda what it is. Basically it means that Nvidia is allowing companies to sell "their"(as in not the reference) GPU as low as 599. When Apple Laptops come out, they don't allow retailers to sell them for whatever they want. Best Buy can't list it as a doorbuster for $100. There is an MSRP, which is suggested retail and a MAP price, which is as low as they're allowed to advertise it. It seems like this is what Nvidia is doing. They think "their"(Founders Edition) card is worth $699, so that's where they are selling it. If their partners want to have their own design, and sell it for $599, great. That's on the manufacturer to cut costs and sell it for $599.
Now if it comes out that Nvidia is charging their partners to the point that it's financially impossible to release a card at $599, then we can grab the pitchforks. Nvidia believes that their "Founders Card" is worth $699. Not because it could possibly be the only card on the market, but that's what they think it is worth. Now the partners can have their AC+ Kingpin edition, or whatever, at $750, $799, or 599 or whatever they want to price it at. They also have the option to come out and throw a cheap fan on it and sell it for $599.
It's not likely you will see one of those wizzbang OC+ mega superclock cards coming out at $599. Their partners will release them based on the standard that Nvidia has set at $699 (so they'll be better....more expensive).
Also, in one of JaytwoCentz videos he says that he has reviews coming soon from all the board partners. So take from that what you will, they could all be "Founders Cards" or something else, but it seems like he has them currently.