Up until the 10/18 rankings, the teams were ordered by polling coaches around the league. But now they've crossed over to using computer rankings, which will be they way it's done all the way to nationals. So comparing this week to last is really an apple/oranges situation.
Honestly, I think they should just put out a preseason ranking based on a poll of coaches, then nothing until the computer is good to go. It'll spare everyone a lot of confusion, be less work for whoever administers the polling of coaches, and nobody will care by the time it actually matters (nationals selection in February).