Well, our pals over at Electricpig think they know the answer: there's a full-on stereo Bluetooth headset on its way. The new iPhone 3.0 operating system enables stereo Bluetooth, so it makes perfect sense that Apple would replace the old single-channel headset with a new stereo model. We'll keep our eyes peeled for more.
That said, over at AppleInsider there's some speculation that Apple may be recalling the old headset for "undisclosed reasons", suggesting there may have been some technical issues with the gizmo. But that's, frankly, not the explanation we want.