It appeared that there were 3 spots available to 4 players: Slater, Ventrone, Lew Sanders & Spann.
Slater stayed because of his WR/FS/Return versatility, and his draft status.
Ventrone stayed because of his FS/ST experience, and his potential at Slot WR, esp. w/ Welker's availability in doubt.
Sanders stayed because of his CB experience & his possibility at FS.
As well as Spann has played, we just can't keep them all.