You don't have to buy the monocle. Please shut up.
Seriouspost though, the prices do seem a little high; I would never spend $70 on a vanity item. Sure, I would spend a billion and a half isk if I wanted something, but I'm old and rich and it's not real life money. Other microtransaction games (specifically global agenda, which I've been checking out the past few days) sell functionless vanity items for like $5. At that price the monocle would cost 100m isk, which would greatly increase demand. I would probably get one just to check it out.
The key concept here is profit maximization. When selling things you don't want to set the price too high or too low. If the item is free you make no money no matter how many units you sell, and if the item is too expensive you make no money because nobody buys. I suspect eve's vanity items are strongly toward the 'too expensive' end of this continuum at the moment.