There's not a 'market release', per se. It's not going to be in stores, according to Frogboy and Kryo. You can either purchase it separately as a digital download/physical CD shipped to you, or you can get it in the 'Ultimate Edition', which is download only.
Hmm. I wonder why this is the case - I suspect the retailers made them [url=http://blog.wired.com/games/2008/04/exclusive-inter.html]an offer they had to refuse[/url]:
We had a meeting with GameStop to talk about selling a boxed version of the game. Once we had a bunch of episodes together, we would collect them and put them in a box, you know? And GameStop said, oh, that's fantastic. We'd love to do it, we'd love to carry the game... but it's not going to be available anywhere else, is it?
And Robert said, well, we're going to digitally distribute it first.
They got really upset. And they said, no, you can't do that. We can't have it in our store if it's coming out digitally first. And he said, well, I'm sorry, that's the way it works. We're publishing our game and we can say where it goes. And so the deal that they tried to strike with Robert was okay, well, listen: If you cut us in on the profits from online distribution, and XBLA, and everything it comes out on, then we'll think about carrying it in the store. Just, what assholes.