I can see where your friends is coming from, as I've also had that idea. When turned into movies, things are often left out or cut short. If a given game were to become a television series, however, the producers and directors and all them could leave in (or even add) as much as they want, or as much as they feel would serve said game justice.
Possibly one of the biggest obstacles when making a movie based on a game is the time constraint. You can't have an eight-hour long film, now, can you? (Well, I suppose you could, but who's going to sit through all of it, really?)