New map of cold hardiness

The USDA has released new plant hardiness map for the US. I am still in good old zone 5, so no lemon trees for me.I've heard that the fun does not begin until zone 8. Apparently, there are 2 mechanisms of cold resistance in plants and the first one only provides damage protection down to that zone.
Also, most of the United Kingdom territory is zone 8. Now I know why British gardening books look so ridiculous sometimes (Wisteria pruning in January? Hello??)