Yes, that is correct. The collection of duty is core business for Canada Customs and they only collect Federal and Provincial tax as effectively a sideline or a favour to other government agencies.
RFD people's experience is all over the map.
Some claim they have been crossing the border for years with major purchases and never been asked to go inside and pay anything.
Others have more realistic tales of periodically being sent in for day trip purchases of as low as $50.
It varies by border crossing too. Smaller points of entry tend to send more people in, but even there it can still be a random process depending on how busy they are or on individual officer.
Once inside, some officers will be quite adept at looking up duty rates and charging accordingly, while others will take a guess that an item is zero duty and just collect the tax.
One indisputable fact is that with the ever increasing traffic over the border they are not able to operate by the book nearly as much as they used to.
Years ago Canadians seldom went over for a day trip to shop, just for overnights or vacations.