I think more than advertising, it's the slippery slope of offering a somewhat expensive peripheral on top of the core system years into the console's life cycle. On one end, you're going to have people who will put off buying one because of the price and chance that it won't be supported, and on the other end you have developers/publishers who won't require it or even utilize it because they're worried not enough users will have it, and requiring it will hurt sales. Anyone on the front line of this release who spends tens of millions developing some triple A hardcore title that requires Kinect is going to lose their ass on it, and they know that, which is why you haven't really seen anyone announce anything like that for it yet.
Again, if you look at the Wii, High Voltage is doing very little to utilize Motion Plus in Conduit 2, and they're definitely not requiring it at this point (and they should), and it's a $20 add on that has come bundled with some million plus selling games on the Wii like Wii Sports Resort and Tiger Wood '10.
If 3rd party developers are nervous about not having enough people buying a $20 attachment for a Wiimote, imagine how quickly they're going to balk at spending a lot of time on developing for a $150 one. You can be sure that companies like Harmonics who are making full games requiring Kinect are having some substantial money thrown at them from Microsoft. This is going to be the case for the life of these motion control products from Microsoft and Sony, either they produce enough 1st party games to encourage/require people to buy the hardware, and/or they pay off outside developers who normally wouldn't consider it from a financial standpoint.