I don't think your link has the complete story. You can find lots of information about this issue with a google search for facta (the name of a new US law that's trying to pull more people into the IRS dragnet) but here is one article that lays it out fairly succinctly:
U.S. citizens on the other hand, have an ongoing obligation to declare and report their worldwide income to the U.S.A., regardless of where they reside. U.S. citizens who have permanently departed the U.S.A. and have become full-time permanent residents of Canada are still required to file U.S. income taxes on an annual basis with the Internal Revenue Service (IRS). The only way for U.S. citizens to avoid this would be to go through a process to renounce their U.S. citizenship, which is not practical or desirable for most people. Therefore, a U.S. citizen who resides in Canada is essentially subject to the same U.S. filing requirements as they would if they continued to reside in the U.S.A. This means filing U.S. Form 1040 every year, and reporting worldwide income.
The bottom line for U.S. citizen residents of Canada is that they must file two returns each year â" a Canadian income tax return because they reside in Canada, and a U.S. return based on being a U.S. citizen. The Tax Treaty between Canada and U.S.A. has several mechanisms available know as foreign tax credits, to make sure the person does not have to pay duplicate taxes to both countries.