You did some great research. I hope to see more in the future. It is very helpful for my purposes. You are indeed right. Managers need to be much more involved in the recruiting and hiring process.
Few companies seem to believe that, and fewer still expect it.
We can blame managers for abrogating a key responsibility, or we can blame HR for making political hay in this situation. I've seen more HR executives fight to maintain control over hiring than I've seen them work to help managers learn to do it for themselves. It's a nasty cycle that's getting no one anywhere. Recent reports in other technical publications reveal that some corporate departments, notably Information Technology, are taking the bull by the horns and hiring their own recruiters, rather than trusting HR to manage recruiting. I believe we'll see this trend expanding into many more corporate departments.