Wrong, yes. But absolutely normal.

All exchange services, be it Thomas Cook, Travelex or AMEX have much higher fees airside than they do landside. They justify it with the "extra costs" of operating inside the sterile area (and granted, there are some, but they're not THIS high), but really, it's just a way of milking unsuspecting (and often novice) travellers.

They can usually get away with it once for everybody. Then people tend to wise up and look for the kiosks outside.

Or use ATM cards, like tom911 suggests. Provided you take out a fair amount each time, since banks charge per withdrawal, it's the cheapest option.