The diaper creates a tight seal around the soda can allowing the soda to be launched out the barrel at high velocity. Of course they didn't have to use diaper, a hand towel would have worked too.
I concur, but offer as evidence to their freshness the fact that a dog ran up to one, sniffed it, and moved on, instead of immediately chowing down. Dirty diapers are Doggie Happy Meals.
The manager at one office I worked at had an actual "Air Cannon" as in, it would shoot an actual shock wave of air about 50 ft. Nothing like crunching away at a cubicle when suddenly and silently all of your papers blast into the air.
Look how the white dog, which undoubtedly symbolizes the Id, runs after every projectile. Its curiousness is unrestricted, except of course by his owner: the symbolic ego. As you can see there are other dogs in the video that are restrained greatly by their adherence to their super-egos. Thus, any natural response they have is met with immediate disinterestedness, and practically no reaction.
In conclusion: the white dog was poorly trained despite listening to commands; the other dogs were beaten by their owners, or paternal authorities; and every person in the video wants to fuck their cousins.
Somehow they will perfect this technology and you will see it at every furry convention across the country. It will be just like the T-shirt cannon at football games, but perverted.