http://www.kenrockwell.com/nikon/d3/h3d-1.htm: “For those of us in the press (Ken), we laughed when we looked at the EXIF data of Nikon's PR photos of the D3. They were shot in a studio, so of course Nikon had them shot with an appropriate camera: a $30,000 Phase One P45 back.” Anecdotal evidence, but I'm unable to find another source, so take it with a grain of salt.
If on the other hand the pictures are about showing what kind of results the camera can produce then I very much doubt they'd risk faking it by using a different camera.
Though will we consider a deceit if the camera used is the same P&S model, but lighting is set up? And then there's extensive post-processing, which is possible and may alter shots significantly.