It's true about Florida. Drive up the east coast, once you drive though Palm Beach county (heading north) and into Martin county, you'd swear you were in Georgia. It's a sudden change. Even environmental. Since zone 10 (topical) ends somewhere near on the border of Palm Beach and in Martin counties.
Edit: Correction. Zone 10/9 are expanding. Which makes sense considering global warming. See http://www.garden.bsewall.com/topics/hardiness/maps.htm