Some blogs are claiming that Kim K. might have used a body double for her Superbowl commercial, since her bottom half doesn't look as voluptuous as usual. Guyism swears that the body we see in the commercial isn't Kim's, if you compare recent photos.
I had to look over the video a couple times, and I must admit her butt does look unusually small. It looks like they used a body double for close ups of her body, and that's probably why we don't see her face. But, then again she is wearing spandex.