Lifedoom, that is mainly due to the way the tax systems differ comparing the US to the EU. Simply put, the import taxes here increase the price so that there's almost a $1=1€ conversion rate when it comes to computer parts, even if the currency conversion works out at $1=0.78€. The conversion for GBP is around $1=1.2£ (as you seem to have figured out). It's a bi-product of the mentality that trade within the EU should be "free".
This is a bit of a side-track but I'll touch on it anyway because it's related:
If you were to import a product from the US there is a large risk that you need to pay tax on that imported good. In Sweden, the import tax is 7% of the original price, and then they add 25% (MOMS, or VAT) to the estimated original cost of that product (in Swedish: anskaffningsvärde). So, if you bought something for 1000 SEK (after currency conversion) from the US you first need to add 7% to that total cost (70 SEK) and then 25% to the original cost (which can be anything, if the product is 2500 SEK in Sweden with a "recommended price" of 3000 SEK you need to pay 25% on the 3000 SEK). The total cost in this example would be 1000 SEK (original purchase) and then an additional 820 SEK, along with the shipping cost of course.
How the above works in GB I have no clue, but there are means to avoid this tax. I won't go into that here because it's basically fraud.
Is it worth ordering from the US then if the price ends up lower (or close to the original price) even with the tax added? In my opinion, no. The simple reason is that within the EU you have some perks that you simply don't get if you order from a different continent. These can include (but are of course not limited to) right to a warranty claim by law, RMA service if the product arrives DOA, and so on. In some countries/cases you have a short period where you can choose to send back your product, unused, at no extra cost and get your money back. You are also protected by EU law when it comes to transaction and privacy details (which also holds true if you for example where to use your country's iteration of Ebay).