I don't know about the Inuit, but "gravad" fish (fish buried and fermented near the tide mark) has been fairly common in the Nordic countries as well as in the Baltics since the middle ages or before.

"Rakfisk", a Norwegian variation, could be left to ferment up to a year. Iceland has Hákarl, - fermented Greenland shark that is also left for 6-12 months: "http://en.wikipedia.org/wiki/H%C3%A1karl containing ammonia (the process is used because it is poisonous when fresh).

My total guess is that it's more about having access to a wider range of types of food throughout the winter, when many other dietary choices disappear. Traditional food in the Nordic countries at least is very centered around processing that allows for longer term storage, and I'd guess Greenland has much the same.

That second link should be the experiment I was referring to. I remember reading an account of it that one of them did run into some vitamin deficiencies which they realized were because they'd been excluding a particular type of partially-rotten fish dish that normally provided them.