Let's get this out of the way. "Webcam" for almost all discussions is a cheap thing built for disposable video use.
16 bit video channels are mostly for scientific use like Hubble and research so for that you look at the usual 5 and 6 figure cameras.
Then again you may want to reveal EXACTLY what you are trying to do.
Does anyone know of a current or recent webcam which outputs 16bit YUV with very good low light capability? (May 2010)