I think the "don't use admin username" is an overblown precaution and fairly worthless (by itself), as the username, regardless of what it is set to, will always appear in the URL for that user's achive page. In other words, the administrator username is not as obscured as one may think.

Better advice, IMO, is not to post articles using your administrator login and only use an author account for that. At least the administrator username will not be visible anywhere on the site. And, regardless of all of the above, even better advice is to always use strong passwords - something that the article you linked to overlooked.

Other than that, I agree, it is always useful to be reminded of basic security precautions.