same thing happened prior to BC and WotLK, players rerolling classes, coming back into the game, restarting to play wow again. deviate recipes on my server were 30-100G for about 2 months, then they dried up due to lack of levelers in the barrens, and until last patch were on avg 500-1000 on horde and 1200-2000 on alliance side
drop rate hasn't increased, imo...it's the class combo rerolls and the shear number of players again in northern barrens is amazing. tons of troll druids/locks, tauren paladins/priests, etc etc. when i was leveling a rogue from 13 to 22+ in 2007, i got a recipe off harpies sold it for 150 gold, got a recipe off the theramoore guards doing ratchet quests (learned it), got a recipe off bristlebark mobs doing quests in southern barrens.
once cata rolls, prices will climb again as barrens levelers slow and barrens becomes a ghost town