I agree with your theory. Here's my reasoning. The people marketing the movie have every reason to pack as many exciting bits from the movie as possible into the trailer. (This is why sometimes the trailer is much better than the movie--there are times when the movie only has enough exciting bits to make a three-minute trailer.) So if the *trailer* is boring, that either means that the movie makers could only afford clueless marketers, or (more likely) that the movie doesn't have enough exciting bits to make a decent trailer. Either way, staying home is a win.