I agree with your analysis, but rather than go to the trouble of protecting
plants I find it is best to purchase plants that are rated one zone colder
than where I live. This works very well for me as I don't live in zone 3.
People here plant hybrid roses in a hole and then cover the plant with 9-10
inches of bark which the roses have to grow through year round. That way you
don't have to mulch them every fall as they are always in their mulch. We
can do that because we live in an arid climate and they don't rot.
Sometimes all one has to do is water small plants like tomatoes and then
cover them as the heat from the water will suffice. Occasionally though our
first frost is a 3 day snowstom with temps in the lower teens and then, not
much will save the tomatoes. The advantage of small plants is that they are
easily replaced (if common). It often depends on where you live as there is
"no one size fits all solution" to growing plants in North America. However
there are lots of regional solutions.