Unconscious iteration of this phrase is a common trick. It may be presumed that there is more than one reason for this. One, which affects journalists more than officials, is that the writer wants to show off. When Macaulay says that every schoolboy knows something that most of us have never heard of, we are impressed by the omniscience of a writer to whom such things are a commonplace of the school-room. In the same way a journalist may use of course to impress his readers by showing his familiarity with an out of the way piece of information or with great personages, a temptation to which gossip-writers seem specially susceptible.
But the official is more likely to overwork of course from genuine humility. He puts it in so as not to seem didactic: "don't think that I suppose you to be so stupid that you don't already know or infer what I am telling you, but I think I ought to mention it". Sometimes of course is wisely used for this purpose — if for instance the writer has good reason to say something so obvious as to make a touchy reader feel that he is being treated like a fool. It is better in such circumstances to say "of course" than its pompous variant "as you are no doubt aware". But the danger of using of course too often is greater than that of using it too seldom.