Ah, I discovered the big point of confusion.
In some articles, it's being described as a comparison of the carbon footprint, in some articles (including the original New Scientist article here:
http://www.newscientist.com/article/...et.html?page=1), it's described as a comparison of eco-footprints. Big difference between the two, and really sloppy by the Edmonton Journal and other sources that got them mixed up.
Which is why some people are saying that the tailpipe emissions aren't counted. The eco-footprint argument they're using looks at the amount of land required to raise a dog, assigns a hypothetical maximum amount of energy that land can produce, and then compares it to the amount of energy a car consumes (without even looking at the issue of CO2 emissions).