Yes, you are reading this right. Major Nelson has updated his blog post about the one-week delay of Destination Arcade to let us know that it will only be available during the Summer of Arcade run. For those not keeping count, that's July 21 through August 18, just a few days shy of a full month.
The purpose? Well, right now, there is none. But seriously, what the shit, Microsoft?
As one commenter pointed out, this could be a nonchalant open beta, and Microsoft would make it fully available alongside Kinect later this year. If that's not the case, then it's absolutely backasswards.