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 
eh, the lower end canons have a whiny sound, and the 5d2 has the most clunky sound ive ever heard.
nikon is more of a click.
But i agree, the sound doesn't matter in real life, but i guess it does on a tv show!
anyway, yay canon for their subtle shout out!