On average, an NFL team only has six first round draft choices playing on the team that drafted them. With the recent release of DeAngelo Williams the Panthers are one of many that have five, three on offense and two on defense.
Some bust, some get injured, and some do so well, that they leave via free agency....but mostly, they just get OLD, and have to be replaced. An NFL roster will suit-up 52 players on game day, but only about 10% will be made up of their former first round picks.
Of coarse,"steals" can be found at nearly every position: Tom Brady in the 6th round, Marques Colston in the 7th, LT Jason Peters went undrafted.