Ideally I want a hiring "fun"-nel where a 6.2 can learn the skills necessary to become an 8.3 (or show that they've been an 8.3 all along) through exercises or reading assignments. Sort of an external training/hiring funnel. If nothing else it may also help as a way to build internal training processes and advertise the to the world some of the neat stuff you are working on. I think this is how Matasano recruits and it makes a lot of sense to me.
Pretty much no matter what there is a learning curve associate d with bringing on a new hire. Finding candidates that will attack those curves with gusto is key to building good teams, I think at least. Technical skills can be taught and refined, gumption is a bit harder to instill.
If potential employers divulge shortcomings in the interview then they may be slammed with a discrimination lawsuit.
If potential employers keep their mouths shut, then the overall incoming workforce takes longer to understand the rules of the hiring game.
At the CV stage you might be a 6.2, but the error bars on whether you're a good hire might be +/- 5.8.
As you progress you're not just filtering, you're also trying to reduce the massive degree of error.