An argument for hiring junior developers

I was not aware of an argument against hiring junior developers. It seems to me that companies find it way more desirable to hire recent CS graduates rather than a developer with extensive experience.

The problem I see with the article that it confuses experience with talent. Or at least ignores talent. Referring to your example, it just may so happen that the right Junior Developer has the skill sets to immediately tackle the difficult 20% with little or no mentoring. To me, this is the big reason for hiring junior programmers: their ability to quickly infuse the organisation with new ideas and talent and in the process raise productivity.