It's got a lot to do with how the Disney websites are set up with geo-fencing. If you try to go to
disneyworld.com on a UK based computer or phone, it redirects you to disneyworld.co.uk, which at initial glance looks pretty much identical to the US version of the site but with prices in pounds and UK specific offers. However as you delve deeper there are some features missing, such as certain types of reservations aren't available (no link to them and if you try to manually type the address, you just get a Stitch broken page) which are only fixable with a VPN.
For example, the page that's been linked earlier in this thread about the Tier lists does not work from a UK computer - it redirects you to a page about Online Check-In for hotels instead for some reason. (On that note, if someone actually can copy and paste the full tier list here rather than just a link to a page I can't access, I would be very grateful!)
Similarily if you use the
MDE app from the UK there are some things that don't work; certainly until recently you couldn't check live wait times for instance - probably something you don't really need to do, but it was nice to be able look at in the run up to a holiday to get an idea of what rides to expect to get the busiest and when.