what i see from the article, is that Microsoft is being really-really smart in its marketing strategy...
it had been 6 years after windows XP had launched, and MS hadn't brought a new OS in the market... their "dream project", Vista, was looong due, and they knew it was way from being totally finished. They were under extreme pressure from the market, and they had to launch Vista, while it was still very raw...
They very smartly have given themselves 2 more years to complete the project, and they would continue working on the OS, and hopefully, Vienna, would near perfection...
This way, they can accomplish the new operating system, which in my opinion, would be quite good, and at the same time, remain active in the market (because of launching Vista)...