The problem with all the movies, from X-men to Lord of the Rings, is that they really only *do* focus on a few characters. LotR has Frodo, X-men has Wolverine...not everyone is the main character. In a game, the challenge is to make everyone feel like the main character.
But this isn't a problem with adventuring parties. It's a problem in trying to use the game to tell a story *instead of* to play a game. Movies and TV shows need main characters to ground the audience to one person that they can feel sympathetic to. Games don't....each person's character grounds the audience (the players) and they can feel sympathetic to them. A good DM's job is to make them *all* feel like central characters, focusing on one character just as much as the other, and making sure that they are *all* there for the final conflict to save the world, not just one, two, or three people, but *everyone*, for their own epic reasons.
It's a lot more like a movie where four different, unrelated, insignificant people all have one event which links them together for some reason. One big thing. It's not mostly about the characters, it's mostly about the event, the challenge...that's where the game is, that's where the story should ideally be focused. That's not to say that you should ignore character development, that's to say that character development shouldn't be a huge and isolated goal of the campaign. The story may be based in the characters, but it's more than the characters.