Video chatting uses a lot of data anyways, why would you want to use more? 2.0MP FFC would destroy your data bill, you'd use up the entire 2GB in a short time (or whatever amount you want to pay for).
And for a source on it using more power in a bigger camera, it's common sense. Bigger=more power usage in most cases. I can get a digital camera that runs off of AA batteries and use it at a lower resolution and it would last longer, and take up less space. Obviously for pictures, bigger resolution means higher quality picture, but in the case of video chatting, you can't see that many pixels. 960x540 is the screen resolution size (on a qHD display like the Bionic), and 640x480 is the camera resolution size. You really aren't missing a lot.