From what I've heard from hiring managers, when you open a position and interview applicants without the use of headhunting, the majority of applicants are wildly under-qualified, even if they do have some relevant experience.

Also, I see no reason not to combine both a background check and a technical interview. You have no way of knowing what someone's actual contributions to a previous software project are, even with a background check; maybe they were about as productive as an observer even if they understood the project at a high enough level to explain it.