US have just decided to keep VOR's for the forseeable, as GPS is too easy to jam. The signal is so feeble that anyone with a low powered device in the boot of his car could shut down a terminal area with ease. The RAF have conducted frequent GPS jamming trials involving large chunks of the UK(all on notams) with a great degree of success judging by the blank display on my GPS during one such test.
Not sure about 80N to 80S being useable for MAG headings on an IRS system btw. Its 73N to 60S according to my paperwork but maybe there is some upgrade .....I reckon I'd prefer to be in True no matter what if I was that far up(which I've never been so i cant possibly comment further)