For Microsoft to release a commercial license they have to be able to support it. That means relatively no bugs, staffing tech support, etc... I don't think Microsoft is ready to do that with Kinect.
In fact, I think this SDK is a response to the homebrew solutions that were coming out. I think Microsoft saw the focus shifting off them and onto the open source community and they didn't want to lose the good PR. Meaning this SDK was probably rushed out the door (and I'd suspect has some serious bugs in it)
While I concur to the premise, I must disagree with the drawn conclusion.
At the risk of speculating, I'd say MS need some more time before the release the commercial license, for the reasons mentioned by you (robustness of the code, staffing tech support etc.) and also to possibly see the reception of the software by the developer community, before deciding on commercial terms (It IS labelled beta afterall).