>The 'over many years' is the main point here. At the moment it looks as if they wand to do it in one year.
They're looking ahead 3 or 5 years and also factoring the 'hit' of last year or so based on getting their previous estimates of currency fluctuations badly wrong - MS analysts certainly weren't expecting a Brexit vote. This is no different from other US providers and suppliers. The Pound will remain low, it will most likely drop to around parity next year.
If only for PR's sake, they should take a leaf out of Amazon's book and simply charge explicitly in Dollars + local tax.