My guess: GB not a mass-market product
As long as we're all guessing, here's my thoughts . . .
An app for music creation/manipulation (i.e., Logic, SoundTrack, Reason, etc.) is NOT a consumer (mass-market) product. Some of you believe the average joe writes their own music and/or wants to record their own music, and that just isn't the case. I'm a writing/recording musician myself (Platinum 6 rocks!), and the average joe has no more clue about music production than they do nuclear physics. Yes, there is probably a market for another cheap (<$100) audio app, but it's not nearly large enough for Apple to bother with. Keep in mind that Logic has multiple price points, all the way down to $229.
Others have speculated about GB being a tool for bands to submit their music to iTunes. It just might be, but again, it doesn't seem like a mass-market product that would make a big splash. And it wasn't that long ago, at the rollout of the Windows ITMS, that SJ trumpeted the fact that ITMS contains only "quality" tracks, as opposed to other services that allow any garage band to upload tracks for a fee. Would seem a bit strange for him to change course so soon.
So I'm scratching my head over what this new product will be . . .