I think they even used a nikon in that same episode. Or at least they did in the next one. I think they only use nikon cause, lets face it, nikon has a nicer shutter sound. - That happens to be the best feature of a nikon BTW.
I disagree! I heard a D700(?) shutter this past weekend while at an aviary that a Nikon guy had and it sounded really obnoxious. So loud and clunky. I think the Canon's have a much better sound.
In general though, I care less how a shutter sounds