Usually it's triggered by something else, they smell something, or something isn't quite right......
Then I think we agree more than you think.
As far as your other scenarios.....I think they can learn to look for danger in an area......a certain tree.....certain trees in a certain area. The blind is a prime example.
But to wander through the woods looking up for hunters? I'm just not buying it. I don't think they're capable of that type of thought process.