Understanding rosters takes a little work. I'm happy to do some of it for you through the files I make available periodically.
A few quick roster-related notes on the four NFC West teams:
Arizona: The Cardinals are carrying one more tight end and one fewer defensive lineman than usual. Alan Branch's ability to play defensive end or nose tackle in the 3-4 buys the team flexibility. ... The Cardinals have the fifth-oldest defensive starters in the league. Teams running 3-4 defenses often feature older starters, although that is not the case with the 49ers.
San Francisco: The 49ers are carrying one fewer running back and one fewer tight end than usual, a surprise given their priorities on offense. Their numbers in the secondary are high, continuing a trend set under previous head coach Mike Nolan. ... Barry Sims' presence in the lineup at left tackle drives up the offensive starters' average age, but this is still a young group overall. ... The 49ers have 33 of their own draft choices, tied with Green Bay for most in the league.
St. Louis: The Rams are light at running back, allowing them to more easily carry an extra offensive lineman. ... Only the Bucs and Chiefs are younger than the Rams on average, although the St. Louis starters rank 16th-oldest in the league thanks to Leonard Little and James Hall in particular. ... The Rams entered the weekend with 47 players younger than age 30. No team had more.
Seattle: The Seahawks have only six linebackers, allowing them to more easily carry nine defensive backs, one more than they have typically carried in past seasons. ... Seattle drafted all five of its offensive linemen projected to start in Week 10. That is unusual, although the 49ers would also have five if left tackle Joe Staley weren't injured. ... The Seahawks drafted 10 of their projected starters in the last five drafts (dating to 2005), trailing only the 49ers (12) in the division.