There are two uses of the word troll. I think you are using the less common of the two.
Yeah, trolling can be used to describe people who lurk 24-7 and hop right on posts all day long.
More often, trolling is about the attitude. Is somebody just laying down flamebait all day long?
Are they pointing out the negative parts of what people say and ignoring their valid responses?
Mostly people troll either for self satisfaction. i.e., making easy jokes and doing things 'for the lulz.' Otherwise, they may be working on some type of imfamous fourm reputation that the kids all think is so cool.
Meh. Trolls have their place. Some people take it too far. Some people aren't trolling. They are just assholes. Trolls are almost always trying to be funny. Often at the expense of other posters.
/wall of text
//$.02