Hmm, it is in most cases.
Like, if I gave you this link ( warning! some bad language ) saying "THIS IS LIKE THE BEST AD EVER!!!!!!", you'll think "Wow, that must be really awesome", have high expectations and won't be as amused as if I simply gave you the link saying nothing.
The situation is very important for humor. Today in class, I laughed when a man went by our classroom with a loud lawnmower and my teacher said "..could you try shutting the window perhaps? We could of course shoot the man, but let's stay peaceful."
If a comedian made a joke like that on stage, not many people would be amused because it's situational humor.