Why do Apple charge Brits the same in £s as they do US citizens in $s?
I'm not 100% sure about the UK, but most EU prices include VAT, whereas US prices are displayed exclusive of taxes. Also, Apple does not modify prices every time exchange rates fluctuate, it has to ‘pad' the prices to nullify that risk.
Takeaway/gratuitous pun: Because of these factors, it's not a straightforward ‘apples-to-apples' comparison.
Note that the US Apple Store shows prices without sales tax whereas the UK store shows prices including sales tax (VAT). UK VAT is currently 20%. The current £:$ exchange rate is about 1.3 (November 2018). So there is currently about a 10% difference.