Yes. I totally agree with you.
And also people decide to see a movie a second time or not based upon how much they liked it, and those second viewings can impact the box office (e.g., titanic). Both of these factors have a big impact on "legs" - how much the movie makes over time. And therefore, both of those account for a great deal of the individual differences in box office. But they have little impact on the opening weekend box office.
This is why so many movies have been so frontloaded. There is a lot of hype before it, the built in fans of it all go see it when it opens, an then there is a huge drop off based on less than positive word of mouth.
But do these two factors account for all of the variation between say $267 million and $38 million? I don't think they do -
People also make decisions - and even pass on word of mouth - about films they have never seen. It is called perception, hype, buzz. There were plenty of moms on their cell phones telling each other that treasure planet wasn't for little kids without ever seeing it. There were plenty of older kids who thought that disney movies were for little kids without going to see it. There was plenty of people who might like a sci-fi or action adventure movie who thought that ships in space looked weird and decided not to go see it without hearing from anyone who saw it. People who never saw it were spreading all kinds of bad word of mouth.
No, it got something like 70-ish fresh from the reviewers, and most of the people I've heard from who saw it liked it, at least something about it or marginally liked it. But nobody saw it to even make the word of mouth. I mean here is a more extreme example - what is the word of mouth on Justin and Kelly - terrible! But nobody actually saw it to make that word of mouth! I don't know anyone who actually saw it -
They opened that movie against the wrong competition, they aimed the movie at the wrong demographic. They pushed hard for the tween set, and when that is your only demographic the only box office you get is 40-60 million (e.g., Lizzie McGuier, Holes, et al.).
So these things impact both the initial opening numbers, and the legs.
Thus, I think it is a mistake to think that 100% of the variation in movie box office is based upon "how good the movie is," not only because of taste of the consumers, but by the fact that people "do not watch the movie and then decide if they will pay for it based on whether they liked it or not."