The writers being online helps a lot with facilitating the attitude, but it springs from the way reading the book or watching the show makes the fan feel like he knows the writer and has a personal relationship with him.
Which leads to fans who want endings changed and write whiny letters complaining and telling the author to make Jill end up with Tom rather than Jack.
Then, there are authors who fail. Who don't meet their deadlines. And the publisher on the panel grumbled about the author who didn't finish a book so they were having a "not-a-book-launch" party. (Only at the party did I hear of the medical emergency involved.)
Fan-fan interaction online feeds it enormously, as they reinforce each other and come up with elaborate theories about what will happen next -- to be dashed. (That's the point at which you really should excise what you like, file off the serial numbers, and make it original. Say I. The panelists approved of fanfic, but I think you need to get farther away to free yourself.)
Then there's the problem of series that are actually books that can't be found in one. The promise to tell a story has not been fulfilled. The panelists were keen on how stories expand on their own. (Then I remember Jordan got complaints about padding as well as never ending.)