It would be wonderful if the world could accept blunt feedback. It is certainly easier to give and more in-line with what most technical people would prefer. However, we work with humans, and we have learned an awful lot about how humans respond to language, especially criticism. The advice here applies to giving feedback to any human, not just superiors. As you spend time working with humans, you learn, perhaps slowly that what you might consider "fluff" is really about helping make your point. Being direct doesn't always, or even usually, work as well.