They sign a lot, but they have guys that just don't make it, either, and they have no problem "cutting" kids, regardless of how heralded they are if they don't cut it.
One thing, too, is they move players around to find a spot for them. I noticed this when doing my research for the Alabama D-Line recruits thread on the football board. They recruit a lot of players that are versatile and find a spot for them if they are good enough.
This was the same Alabama team that booted Alonzo Lawrence off the team, the same Alonzo Lawrence the 'Canes fanbase was drooling to get.