I've heard that a kodak digital camera model had a feature for it to be used as a webcam. But i'm not sure whether it has 720p. But you can use a Canon Video DSLR as a webcam to have a "cinematic" video chat
Kind of ridiculous using a $2000 camera for a webcam.
That's why I thought it would be great using a camera I might already own as a HD webcam if it has HD capabilities. I don't think this is possible though without some sort of capture card. Perhaps a lower cost HDMI PCI-E card would work. They're about $200 new though, which is more than the camera would cost!