I don't really think anyone is advocating bittering every batch of beer with Magnum or anything else. It's noted that keeping on hand and utilizing a hop like Magnum or Warrior for bittering most of your beers is a common practice and can save money, etc.
Of course there's still flavor "left" in the hops after a 60 minute boil. Whatever you use will add at least a little something to the flavor profile of the beer.