U of C Faculty Blog:
I'm going to be doing some occasional posting this fall at the University of Chicago Law School Faculty Blog as a Visiting Associate Blogger guest blogger. My first post is now up: Are Feeder Judges Unusually Ideological? If So, Why?
I suspect there's also a lot of path dependence here -- once a feeder judge first gets the reputation as a feeder judge, the best candidates go for that judge. And they go to the Supremes in part because they are the best candidates.