Expenses are higher in the UK (and generally in Europe) due to e.g. VAT (similar to sales tax) and to scale as other people said. In there US there is "plenty" of everything hence prices fall. In the UK (although the situation might be better than other European countries), resources (servers, bandwidth etc) cost more
Also bandwidth costs more in the uk,and dont forget that their primary funds,are GBP,which is in top rate,instead of dollars. Something similar happen to Euros too. Regards
Id put it down to the exchange rate and the usa market crash of $2 - £1 at the moment. I am from the UK and offer hosting, i have servers in the Netherlands/USA simply because they are cheaper.
Because the US dollar is dropping like hell. It isnt worth anything anymore soon compared to the EURO and the UK Pound. The US economy is not here to stay. The Netherlands is cheap because it has the largest Internet Exchange in the world. Called the AMS-IX (http://www.ams-ix.net)