Steam continues to print money for Valve. I mean, how many video game company CEOs are billionaires? Especially a company that really only made a handful of full games in its existence. Since they have so much cash flow they can do whatever they want. And from what I have heard about corporate structure, they really can do whatever they want. There's no set projects and you can work on whatever you want to work on. That's why we have things like steam box and controller that no one really was asking for.
The writer left a while back and released a basic story online. Some fans have been working on developing it into an actual game but who knows if it will ever come out. Look at Black Mesa, that thing has been in development for over a decade.
I think Valve kept working on it but couldn't ever find the right formula. Gaming has changed so much since 2 and expectations are sky high. It's too bad because episode 2 and Portal 2 were setting up for a great final game.
I wish GabeN would just come out and say it's dead and never happening