Thanks all, most enlightening.

Obviously the regs prevail, but personally I can easily see situations where the YYJ/YVR flight might ditch in the water (there may not be that much choice). Even if there is choice, I wouldn't think that a ditching on water Vs one on land (?forest?, ?populated area?) would be so cut-and-dried in all cases that a prudent airline would say "Life Jackets? Nah, we'll never need 'em".

That said, depending on your definition of AC, I guess they have!

I'll take my own inflatable duckie on my next flight.