I'm sure they do. And I'm sure that often it's probably retirees who move south and want favorite northern species in their yards and gardens. And they might be blissfully unaware of what they're doing. The regular Joe probably has no concept of a southern limit for plants. They think that the farther south you go, the more plants you can grow and that no plants fall off the "possible list." In other words, you can grow a Douglas Fir in Key West.
Many northern species have chilling requirements during winter. Each has X amount of hours under 40F that they require in winter to resume healthy growth in spring. Not every northern species, but many. A couple trees that are staples in the Northeast can be grown well down into Florida, such as Sycamore and Box Elder. Sycamores are also abundant in coastal California. So, fair to say they don't need much in the way of cold every winter, yet, they can take cold if they have to.