Lore has to be something that would not reveal whether Tullius or Ulfric won their little battle. Something will happen that makes Tullius v Ulfric irrellevant, and so history will not even record it.
Which makes one wonder why the hell they bothered including it in the first place.

I can appreciate the fact that in order to maintain continuity they need to only have one outcome for any given conflict, but if they're going to write in a potentially game-changing civil war then they shouldn't downplay who won, as it makes a (potentially literal) world of difference.
If I had to guess as to the direction they'll take it I'd say the Stormcloaks will win, as it's pretty clear that they're setting the Empire up to finally implode.