You'd still have to buy the Kinect. And, I'd think, having useful Kinect-compatible software from other sources increases the value offered by the device, compared with what it would be if only Microsoft's software used it.

Microsoft probably wants to continue with the razors & razorblades model of the XBox. So, maybe it wants to extract a toll from 3rd parties who produce products for the platform. No different really than the iPhone.

I don't necessarily agree with DMCA restrictions on reverse engineering, but I do support Microsoft's right to sell a closed platform.

I just can't see myself flapping my arms to lower a projector or jumping up and down to mute a microphone.

On the other hand, how cool would it be to wave your hand in front of your computer to mute it, or to flip through slides by moving your hands back and forth? Think less full-body motions and more simply tracking the position of hands, allowing for touch-screen like interactions without actually needing to touch the screen. There are lots of things I can see this being really useful for (especially 3d modeling; I recently saw an article about an iPad program which lets you model as if you were working with clay, and I would love to have something like that for my PC).

Waving with my hands will be so much easier then pressing the Down key? All the applications you name really depend on how accurate the Kinect really turns out to be.

Back on the first hand, how frustrating would it be to have the Kinect changing slides for you every time you gesture at the screen?

In general, though, yes, I think there is a lot of room for improvement in the technology that supports presenters (but that's still no reason not to practice and get comfortable with the tech you have)