Honestly, it's not much worse than it probably is at other schools. I remember reading somewhere that most schools have about a 50% attrition rate for their recruiting classes, and I'd have to guess that's pretty close to what BYU's is, which, when you think about the standards that non-LDS students have to adapt to, is pretty good.
The D-Line struck me as by far the worst area in terms of poor recruiting, which is why I went through all the trouble of writing up this post. Even the O-Line, which has caught a lot of grief up until this year, has had a better success rate.
I guess, as someone below pointed out, that QB's has to be mentioned too. Without transfers, we'd be toast at QB under Bronco. Hopefully some of the guys in the pipeline (Mangum, Wilstead, and Hall) change that.