PFM, I may be wrong but I think the reason is :
back in the days when cockpits were painted matt black and Smiths provided the instruments, the british way was to have a ground pointer in the artificial horizon ( these were also the days before this instrument became the "ADI").
Today, most large a/c have sky pointers on their ADI's because that's the way american instruments have, I believe, always been designed, and most of these instruments are manufactured in North America.
I personally prefer skypointers, but it's probably just that I'm used to them.
I don't recall becoming disorientated when changing from one type to another, although I did hear of the CAA at the time expressing concern that sky pointers might be confusing ....well they would, wouldn't they?