Last week was different because Houston was ahead of both the Patriots & Ravens in conference record. Patriots now have the tiebreaker over Houston based off Strength of Victory. Therefore, because New England has the tiebreaker over Houston, Houston & Baltimore's head-to-head meeting comes into play.
BTW: I'm going off of ESPN not NFL.com. Here's how they have their standings and why:
1. New England - AFC East Champ
(Wins tie break over Houston based on strength of victory. Wins tie break over Baltimore based on best win percentage in conference games.)
2. Baltimore - AFC North Champ
(Wins tie break over Pittsburgh based on head-to-head win percentage. Wins tie break over Houston based on head-to-head win percentage.)
3. Houston - AFC South Champ
4. Denver - AFC West Champ
(Wins tie break over Oakland based on best win percentage in division games.)
5. Pittsburgh
6. Cincinnati - (Wins tie break over Tennessee, Oakland and NY Jets based on best win percentage in conference games)
http://espn.go.com/nfl/standings/_/type/playoffs/sort/conferenceRank/order/false
Not sure why but that site is showing a blank page for me.