It is impossible for everyone to know everything about every subject, but because these people know Les Mis inside out there is the presumption that everyone else should do also.
I'm sure there are books, films, tv shows, plays that they haven't seen or don't know too much about.
I dont' get this. I really don't. The poster of the film of Les Miserables clearly says a musical phenomenon. What you do you think that means?
edit to add: having read your reply. I can see what you are 'complaining' specifically, as a almost completely sung through musical versus a sung and spoken-dialogue musicals which you called the 'standard' musical.
Actually there isn't a proper definition of what musical entails. If you don't like it, it's fine. But did you not like it because it's all completely sung through, or because the musical numbers just did nothing for you? There is a difference here. If it's the former, then the production crew (esp. the director) had failed to convince you suspend disbelief that in this fictional world he's conjuring, people in it communicate through songs. If it's the latter, there's nothing much anyone can do about it, I supposed. I feel sorry that you don't enjoy it, because you wasted money and time on it.
I am biased against many so-called blockbusters like superheros movies, or stories like Harry Potter, Twilight saga, Lord of the Rings, Avatars. By default, I always avoid them, until I read enough of the reviews in Rottentomatoes before I decide if I should invest my time on it.
So far, I have not watched a single film of the Twilight saga (though I love the BBC3 series about vampires and werewovles called Being Human), and I've only watched the first ep. of Harry Potter. I fell asleep through the first part of LOTR. The last two I rented it on DVD, so I spent very little and had a lot of control of what I wanted to see and what I consider as a waste of time and energy.