It's true - obviously. Kinect being an optional peripheral means that Kinect games have a much smaller target audience. Game developers pretty much only have two choices:
- Develop a game that requires Kinect, but make it a low budget title because requiring Kinect reduces the number of potential buyers (and thus the expected revenue) by 80%
- Develop a game that only has optional Kinect support. This way, you don't lose 80% of the potential buyers, but on the other hand this will usually mean that Kinect support only gets cheaply sticked on instead of being really an important, intelligent and integral part of the game
Playstation Move (and WiiMotion+) have the same problems of course, which is why I've always been saying that I expect all next-generation consoles to ship with a camera/microphone combination that allows for motion controlled games.
I'm still a bit sceptical though that Microsoft will actually include expensive Kinect technology into the next Xbox instead of cheap and simple webcam-like cameras. Integrating expensive Kinect technology seems odd for a company who was so far very successful with its strategy of being cheaper than the competition by keeping production costs to a minimum.
Kinect couldn't quite live up to the expectations anyway, the whole hype lasted only about 60 days. Like the PS3's Blu-Ray drive in 2006, it would be a huge risk to the console's success. The feature would attract a few customers, but much more potential customers would probably be lost due to the increased price tag. And the traditional Xbox audience doesn't care much for Kinect anyway...
So, I rather expect Microsoft to bury Kinect with their next console. They'll keep the most successful features like voice control etc., but they will switch to cheap webcam-like cameras and try to adopt their skeleton tracking algorithms to this kind of hardware.