I think, they already could release the game, but they really don't want to disappoint us. They wants to make a true high-level game and meet all our expectations. It would be a huge failure to release it now when they could make the game even better. The first impression will spread around and they never could make it better with patches, so they want to release an "already patched" game directly.
And there's Frictional Games, who determine the release date. When they play the actual build and find things to improve, they will instruct thechineseroom to work longer on the game.
When Frictional Games think the game is ready, they will release it, not when thechineseroom wants.
I also think, they know that the quality of a game comes first and that's no shame to work a half year longer on the game, when it's just for the good of the game. It's wrong to release it too early, that could ruin all the impact the game could have. All the work would be for nothing just because they couldn't wait a little time longer.
And we all want a good game, so let the devs work as long as they need. They also shouldn't hurry up, better to work slower, but more professional. Frictional Games also doesn't need the money "now", they have enough money that the release can wait.
Better to wait longer and get a fantastic masterpiece, instead of release it now and the experience is only the half what it could be.
Googolplex