No, it's not. The Florida citrus orchard line was moved about 100 miles south and the coastal mangroves at about the Tampa latitude north were nearly wiped out by the severe freeze in 1986 (which also doomed the Challenger Space Shuttle). They used to grow citrus as far north as Gainesville. Not any more. But not because there are freezes every year now; because the threat of one makes it economically unwise to replant citrus. And that's where agricultural climatologists make their money (and lose it for others ;-)
The reason I say that: you can always have a deep freeze that's unusual in winter. It's like the 100-year storm (which seems to happen every 25 years or so). A 70 deg. F day in New York in January might be just as unusual, but it doesn't cause the same damage so it doesn't get the same press (though the press is noticing the East Coast warm temps, too).
Warm temps in the north only cause damage if followed by cold after plants have either dehardened (remain dormant but more cold-sensitive) or actually broken dormancy (bud swell.)
Florida citrus growers have probably found the "100 year freeze line" somewhere south of Tampa.
Gainesville is probably warm enough for citrus trees to survive 19 years out of 20...but 20 years isn't very long for a commercial citrus grower to have a living orchard, in that 20th year you might have a freeze bad enough to kill the trees outright. I'd guess about once a decade it's cold enough in Gainesville to at least destroy a citrus crop even if the trees would survive. You could plant them in your yard there with the realization they may perish eventually but it's no longer considered worth it to grow them economically.