Huh? I don't get it. "TT" stands for "tenure-track." Am I missing something?
Ah, sorry. I am used to TT (or T2) as a law school ranking. T4, TTT, TT, and T1 being the three tiers respectively. I thought you were talking about people paying their dues in lower-ranked schools before they get hired by higher ranked schools.
From what I hear, this still tends to be true. Many people still pay their dues teaching at lower schools till they get hired by the better ones. That's what happened with the teacher of the Mock class I was in (Buel?), she said that she had taught at another school before UT and that it was pretty typical of teachers to transfer up the ladder of schools.
Yes, this is quite common in academia -- though exceptional candidates do get their first prof job at top-20 schools. Leiter has some studies on this, including a ranking of which law schools are best at placing law profs at "elite" schools -- and for elite, I think he's counting more than the top 20 (can't remember if it's 30 or 40, maybe). Texas does fairly well, especially for a public school -- if I recall correctly, only Boalt, Virginia and Michigan do better.
It's traditionally in your first few years at that "lower" school that you establish your publication record, which is what attracts the "upper" schools.