I've been searching around and can't find any info on this. I know that Westfall is supposed to have multiple types of herbs (Peacebloom, Silverleaf, Earthroot, Mageroyal, Briarthorn and Bruiseweed) but I'm trying to farm my herbalism from 50 to 85, ran across Wetlands loads of times since yesterday and I kid you not, I've only found 2 Mageroyal herbs and 1 Briarthorn. The entire zone is completely filled with ONLY Bruiseweed and searching the info on the amount of nodes that should be in the area, this doesn't right.
So is this normal or a bug?
Some extra info: I did try going to other places - Loch Modan and North Duskwood, none of them really worked for me.
I can't tell from your post if you were looking in Westfall or Wetlands--those are two different areas. If you were looking in Westfall, then I definitely believe you when you say there was nothing but Bruiseweed. You need 100 herbalism to pick that, and I know mine was never that high when I sent a character to Westfall. Probably all of the lower-level stuff had been picked by other players already.
How do you feel about taking a little trip? Go to the Darkshore dock, and take the middle boat to the Draenei starting zone. Run straight north across Azuremist Isle, and cross a bridge to the more threateningly-named Bloodmyst Isle. There are enough herbs there to choke a goat. Silverleaf, Earthroot, Mageroyal and Briarthorn are all over, and I never see any players picking them. No peacebloom, though; I swear there isn't a single one on that whole island.
Make a mental note of where you find them and circle back because they respawn in about a minute.