Hi Seth,
First of all, who said our site was merely "meant to introduce people to the Puritans?" Go back and read the original stated purpose.
Second, those involved in the site either have or are working towards their PhD's in seventeenth-century theology. We often cite materials we do not completely agree with. It's called academic freedom to explore ideas and their consequences and to offer up materials for critical evaluation (which obviously you have engaged in).
Third, and to the point, this is an "excellent" article because Letham demonstrates his thesis that there is some diversity on this issue in the history of the church. While we may take issue with some of the particulars of his essay, the overall thesis stands. Was there not diversity of understanding on the length of the days in Christendom?
Fourth, my posting this article is no more a piece of propaganda for the FH than is our having Dr. Rowland Ward as a part of our team. I have no doubt that he would disagree with the view of creation that I hold to, as well as what I understand of Doctor Jones and Doctorandus McGraw.