I was at the HCSB Study Bible site today and found this new posting by one of the contributors Jeremy Howard detailing the approach to what was included and excluded from the study notes:

Approximately 15,000 study notes appear throughout the HCSB Study Bible. We could have included more. As you can see from the list of contributors, there was no shortage of scholarship for this study Bible. What led us to be so discriminate about the notes we included is that input from study Bible users reflected their desire to have necessary, relevant notes within the context of the Scripture being studied. That meant information – notes, maps, illustrations – should be concise and impactful, plus easy to find. Rather than overwhelming the text of Scripture, the study notes and other aids are designed to serve the student of God’s Word and not distract from the text itself…

It is interesting that the number of notes is less than the MacArthur study Bible, the ESV Study Bible, and the Zondervan Study Bible.  It is not a competition for sure and as I am certain others have found at times – less is more.