1) The AB seems to draw a mainly UK-based crowd, hence why you're likely to get UK-based information more often. Perhaps due to the domain ending in .uk, or perhaps it's more advertised on other UK-based sites?
2) The domain registration system is not connected to server hosting. You can purchase any domain you like, whether it's .com, .co.uk, .co.fr, .de, whatever. You can host that site wherever you like. The idea with the different domains was to make it easier to assess where the company or service is based: .com are for international commercial site (but due to history and USA getting the internet first, tend to be American sites), .co.uk for UK-based commercial entities, etc.
3) The domain (from a whois lookup) seems to be associated with a company in Kettering, silverdisc.co.uk.
4) Tracing the responding server's IP, it seems to be hosted somewhere near Sayreville, New Jersey, USA.
5) Any stuff about purchasing goods and that kind of thing is nothing to do with the domain name or where the server itself is hosted. The rights you have are specified by where the company itself is registered. As I say above, this can be a UK-based company, registered in the UK, and host its website anywhere else in the world, with a domain for any other country in the world. The only issue with hosting elsewhere is that there are separate data protection acts, copyright acts, etc., with information on the server hosted in another country.
Hope this helps.