We just came back here to report on our "progress" (see above) and saw your post.
We have an open case number, the Apple person associated with it has said they see our point and Apple is working on providing the explanation… But no explanation ever arrives, just more monthly reports with inexplicable numbers.
We actually suspect the calculation are correct, and we've told Apple we're happy to have "egg on our faces", but realistically we'll never know. After another couple of months of silence from Apple we've written to them to suggest they just own up and admit they'll never give us the data. They'll probably reply that they're still working on it, as they have been for half a year now, and after that we'll probably stop reminding them every few months the case is still open.
Go email Apple directly, get your own case number, and if they ever tell you how they're doing the calculations please post it to the forums. We wish you luck, but don't get your hopes up.