I don't think so necessarily. QBs want to play and (basically) only one can. Generally speaking, they'd rather go anywhere and play rather than sit. I think Alabama only had one scholarship QB on the roster after the season.
It should help get one each year but not necessarily keeping them around.
Bama isn't pumping NFL QB's out really though, are they?
Sure, some back-ups here and there. But, I don't think they have a starting QB in the NFL right now. Mostly just guys that have had a couple seasons as a back-up and then washed out. (This was completely from memory, I did no research so forgive me if it's inaccurate)
No, they aren't producing much for NFL guys. But they're getting the highest-ranked guys out of high school each year. They just aren't keeping them.