Some responses to the questions raised here, in reverse chronological order:
1) There's a line break in this http://jgoodwin.net/jobs/ graph. The complete sentence is "Where faculty earned their terminal degrees at U. S. News Top 30 programs."
2) I will eventually enter the data from the approximately 120 other PhD programs. I'm using the U. S. News order because it's there, not because I think it's valid.
3) This graph: http://jgoodwin.net/jobs/group.html has a breakdown by rank. Assistant professor appointments show a notably different pattern than full.
4) The chord diagram (http://jgoodwin.net/jobs/chord.html) shows faculty interchange between programs in the U. S. News Top 30 that had at least five exchanges of faculty in one direction or another (hiring or placement). The mouseovers will show you labels when they are omitted.
5) I don't know what's been stated here in recent weeks. The article that Slate references did not, as far as I know, collect data on sub-fields in English. I am. I will eventually have charts showing where rhetoric/composition, creative writing, and linguistics faculty who teach in English departments earned their degrees. These sub-fields affect the prestige hierarchy in English departments, and the Pedagogy article did not address this, which is one reason why I'm collecting this data.