Slow news day, is it?
You're conveniently forgetting shipping costs.
The UK is a lot further away by sea from China, Taiwan and Korea than the State of California, and is inconveniently spread out over a bunch of islands in an archipelago off the west coast of Belgium. Granted, most of its population lives on just two of those islands, but my point is that you have make an additional stop, instead of just calling at Rotterdam. Each stop for a container ship can add up to two days to the journey time.
In the US, of course, they have 270 million+ people all living in the same country, with a neighbour that speaks the same language, so need for multiple-language "Quick Start" guides—economies of scale can be applied easily.
Europe has a Babel of languages, so you need to produce separate runs for each set. (E.g. one run for Scandinavians; another for the north-western EU countries, including the UK; a third for eastern European nations... and so on.) Localisation of software, documentation, packaging and other materials costs money.
However, delivering products to mainland EU does allow for some economies of scale: most countries on the mainland have compatible plug sockets, for example. The Eurozone also helps by eliminating most of the forex issues too.
The UK's large, incompatible and somewhat over-engineered standard wall plug design requires either a separate manufacturing run just for the UK and its dependencies, or an adapter included in a generic "European SKU" package. Neither option comes for free, and the latter has knock-on effects on shipping costs because you now have to pack everything into a bigger box, reducing your volume per shipping container. It also adds to the recycling expenses, which the EU (including the UK) requires manufacturers to pay for.
While the costs mentioned above aren't *entirely* responsible for the price differences in different territories, it's nowhere as bad as you imply. And Apple are perfectly entitled to charge a bit extra for bothering to tailor their products to your country in the first place; it's not their fault you don't live in the US.