Yes, I asked FedEx and I couldn't even ship CO2 cartridges with my bike. So it's not just on passenger aircraft.

My sister's LBS was kind enough to let me borrow a couple of cartridges for the Lone Star Ride and return them when I didn't use them. (She uses a hand pump.)

Which brings up another thing - I deflate my tires before shipping my bike. I think that's probably wise, but I can't remember ever seeing that in anyone's instructions.