A 10 W HID canister and a C8 dive light are rather different animals, and the price differential isn't exactly small!
Needless to say, I agree that there's a huge advantage to HID in the high light output, long duration application. In a few years, though, I wouldn't be surprised to see LEDs start to displace HIDs at the lower end of the range as LED technology becomes capable of higher output. LEDs are cheaper, tougher, and have even better power consumption. I think a lot of the issues with the Light Cannon result from it being at the bottom end of the HID price range. It's still a nice light, but I think for the price difference between a Light Cannon and the eLED, I'd stick with the eLED at the low end of the price range and suck it up and pay the difference for a canister light at the higher end of the price range.