You forget to add Tax to the US price
UK advertised prices always include Value Added Tax of 20%.
US advertised prices do not include Tax, the rate of Tax that must be added to the advertised price at point of sale varies from state to state, Americans know to add state sales tax on to the price they see advertised, Brits don't need to add anything on, as the advertised price already includes all taxes.
Quoting the two prices and pointing out the disparity gives an unfair comparison, since you fail to add GST to the US advertised price, the price paid by a US consumer is higher than the advertised price, the price paid by a UK consumer is not.
If you add 20% to $658 it comes a lot closer to the $807 the UK customer would pay. This means that Apple is making a similar level of profit in both markets (after accounting for daily variances in currency exchange), you cant really blame Apple for making the iPhone more expensive in the UK, the UK Government sets the rate of tax and mandates how prices are displayed and advertised.