What do you do when you are trying to keep symmetry in your device, but only have 2 speakers and a volume rocker to fill the spaces? If you’re HP, you’ll hide the serial number barcode on a popout tab in this fourth space.
Naturally, they could have done something useful with the space. Placing a SD (or micro SD) card slot in this location comes to mind. Possibly, this was going to hold the SIM for the 3G version that was never released. Regardless, it is still odd.
[end of transmission, stay tuned]