Forgive me oh fantasy gurus for what I am about to say.
I'm really, really starting to think that matchups can seriously dictate the success of your team. The "always start your studs" theory is no good when you are fairly certain that they will get stuffed or if you have a better matchup. In a scenario like Denver (awesome running attack) against KC (horrible, horrible running defense), you really have to weigh your options because the chance is there for a huge, huge game. If you are willing to take the risk, you may get rewarded.
Another scenario is when your good WR's are going up against those "shutdown" guys like Bailey, Charles Woodson, or McCallister. Do you really want to have a game where your top guy busts when a lower guy is playing a terrible pass D like Houston, Arizona, or Atlanta?
Now, I'm not saying bench Portis, Deuce, Holmes, LT, or Moss, Holt, or Harrison every time (or at all) because of matchups, but when a major opportunity presents itself against a tough opponent, you may want to take the chance with a better matchup and hope that the gamble pays off. Hey, if you're going to lose anyway, you might as well try to pull something out!