Your example of Fallout: New Vegas? That game was more linear than anything else, being forced to generally take the same path with each character you make.
Did you know that you don't even have to do a single quest? You could roleplay your character as a blacksmith, and stay in the same town doing nothing but smithing and woodcutting. Not even do one quest, or even visit another town.
That's what non-linearity is, not being able to fly over the mountains.
I'm afraid not. New Vegas is the best example of non-linearity in a "Bethesda games studios" style game since the release of Daggerfall (which was the last true non-linear BGS RPGS). Within the quests there were multiple ways to complete things either through a choice or through using a different skill (I.e speech or science). Within the storyline itself it contained 4 separate endings based upon which of the four factions you chose to side with. Morrowind, Oblivion, Fallout 3 and I suspect Skyrim (haven't finished yet) have one single ending. Technically Fallout 3 had a choice or two popped on the end - they kind of ruined that by turning it into a free play after mainquest by a mod.
Unless of course you are also talking about simply being able to choose where to go, which as I explained before means sandbox and is not related to linearity.
Your second point refers to Larping. Yes a person can choose to do nothing more than chop wood in the game. However within the design of the game it is assumed a person will be exploring and completing quests. To say that this indicates 'non-linearity' is therefore incorrect, because it exists outside the boundaries of the intended game design. It is part of the sandbox gameplay, but choosing to complete or not complete quests does not in itself indicate non-linearity.
As you say non-linearity does not include being able to travel over mountains, but neither does it include non-quest/storyline related activities.