We have the most expensive defense in the league on an average per year basis and that is not sustainable over time," Marathe said. "Becuase of the cap, if every veteran on the team took a 15 percent discount on their market value, you couldn't field that team still under the cap because the difference between wholesale (draft) and retail (free agency) is so wide.

"You have to figure out which players to keep and which players to let move on and churn out. Because you have to continue to replenish the system.
[URL]http://espn.go.com/blog/nfcwest/post/_/id/92769/nfl-econ-49ers-sustainability-rams-plan[/URL]

Sums it up pretty well. You have to let some go and draft well.