I doubt that study is about whether it's entertaining to watch other people speculate on a story's outcome when you already know it.
Or, to clarify in a different way:
I find it more entertaining that Herschel (and others) don't know the outcome yet and are busy speculating about it.
And to be honest, I also don't believe that study accounts for the speculation that is possible when people talk about an ongoing series. Such speculation doesn't happen in a movie usually. I will admit that sometimes the final conclusion or relevation is unsatisfying compared to the speculation, but the speculation is its own entertainment.
And in my case, it's more fun if I know the outcome but the others speculating are not.