Many contires have reciprocal tax agreements with the US so that income taxed by your host nation isn't taxed again by the IRS. It may just be a matter of paperwork for the authors of this blog to demonstrate that they've been paying Canadian taxes.
It is very difficult to stop being an American and getting harder all the time. Its like a giant invisible curtain... (like its made of iron or something, heh) Not to keep you from leaving, but to make sure your money can't.