When Deathwing roasted Azeroth, he left fiery destruction in his wake. The volcanoes, tidal waves and rents in the crust changed the ecology of many zones, allowing different plants to flourish and others to die out of certain areas.
Suddenly my Herbalism charts didn't work so well anymore. I've now updated them, using a combination of exploration and the first batch of stats on Wowhead. It's still a work in progress and I'll be updating them regularly over the next month or so, until the stats in Wowhead have settled down and give a better indication of the numbers of spawns in each zone.
Leveling Herbalism: Cataclysm Edition
I hope you find the charts useful as you level up Herbalism!