There are lots of DIY multi-touch examples out there. The difference is that Microsoft, and others, have productized it in such as way that people can actually use them for more than just slick demos like these. All of the commercial multi-touch devices are expensive, up to $50k walls, but no one has been able to sell one of these homemade versions. And, they never will.

Say what you will about Microsoft's offering, they are making strides and are getting developers working on new apps. That's what it will take to make these more common.