There ultimately isn't enough competion in the Market for the companies to want to reduce their prices. I hope the irony of that isn't lost on GW.
BTW, I suppose I may be wrong. AFAIK, this is the genuine reason for the overpricing (perhaps mixed with a little avarice), but if any Aussies want to tell me otherwise I'll take their word for it.
EDIT: omg strewart I almost didn't notice. It's me! The guy who doesn't mind Lvl 6 spells!