Does the same hold for the UK?
It should do, but I am not 100% certain on the manufacturing situation (you guys get it from a different plant generally).
Also, with the 9100 be discontinued in the UK as it has been in the US/Canada?
Nope, at least not yet

. It was discontinued in the US where there is the very similar XPS on offer, as it was not attracting enough sales. Where the XPS is not an option (basically the rest of the world), the i9100 should remain.
And finally, will the MR 9800 ever be available in the UK again?
Cannot say for certain. It could be not included at the moment because of stock situation, because of manufacturing fault/ delay or because it was discontinued. I have no info..... but my gut feeling would be yes, should be back on offer soon (they took the 128MB MR9600 off the configuration of the i8600 here a while ago for about 2 weeks, and then replaced it after stock replenishment, so could hopefully just be the same there).
Cheers,
Stu