Blizzard put a huge investment in their games. They're take a different attitude to other developer/publishers. If a Blizzard game fails, it would carve a devastating hole in their profits. So no doubt they want the game to be as perfect as possible, and release it when it is the best time to maximize sales. Not during the back end of an economic slump.
They haven't gone to beta testing yet. That will typically take six months to find bugs and properly balance the game. You don't want someone picking up the game and 10 minutes later discovering a neat strategy that allows them to get a definite win when playing one particular race. It isn't just a case of shuffling numbers, it might be a the existence of one unit or one pair of units that is an imbalanced combination. They can't realistically make tech-tree/ability changes with patches. It would be a joke.
Players are also keen on finding a new e-sports. Part of the success of starcraft 1 was that, that people could get good, play professionally, and win real money. This made it a
"serious" game. It has to come across that way. As a serious game, many players will take it seriously.
This latest effort will introduce the new battle.net. I suspect they want to make this game much more than just an RTS -- by adding in a strong social networking element to battle.net, making it more like facebook. In fact, Blizzard have said they want to allow you to import your real life identities and real life friends from existing social networking sites.
It's a way of letting you know that your online and real life friends are all playing WoW right now, so why don't you buy the game and join them?

Even when out of the game, you may have a battlenet instant messaging client popping up every 10 minutes with one of your friends begging you to "come and play dota."
This will be more than just the game you see in the video.