The mystery in the case was Justice Ginsburg, who joined the Stevens group, as she consistently has, in applying the Sixth Amendment to the guidelines. She then provided Justice Breyer with his fifth vote to preserve the system's architecture. She did not write a separate opinion to explain herself. The court took considerably longer on the case than had been expected. Many people thought a decision would be out by Thanksgiving, and it is possible that Justice Ginsburg's vote, and therefore the outcome, was in play until late in the process.
Oh, how I hate when that happens! You have a lengthy case, with multiple confusing opinions, and the one person who could explain why it came out that way is not talking. And you want me to read this? I protest!