That's strange..then why is my iPod flashing "Charging" right now. Are you saying it'll never reach a full charge through the keyboard? I could have sworn that it has before...
There's no reason why they couldn't simply add a hub built into the keyboard. Is there?
If it's charging, it will reach a full charge, just like if you were to plug it into any other non-powered USB hub (pull the cord from the back of the hub that leads to the wall wart and you will generally get an unpowered USB hub). It will just take longer because it's not getting the full USB spec of power to it.
It's simple math:
The computer supplies X watts of power to the USB port. This amount is defined in the USB spec; if you supply more you are out of spec, and if you supply less you are a "low-power port".
The keyboard needs 'y' watts of power to run itself, including the USB hub electronics (a very small amount, but not 0).
Thus, the amount available to
all USB ports off the keyboard (really, off the hub) is "X - y". If your mouse is taking up "z" watts, then what's available to the iPod is "X - y - z".
Now: "X - y - z < X" is true so long as "y" and "z" are both positive numbers (which is always true). Since anything less than "X" marks the port as "low-power" ... well, it's low power.
To get around this, a "powered" hub will have a plug into the wall, which supplies power "P" sufficient such that all hub ports will have "X" watts available at all times.
Apple
apparently allows the iMac USB ports to go out of spec when the "new keyboard" is directly attached (presumably not when attached to a hub). The "P" power source is over the USB cable instead of through a separate power cord, but this allows the new keyboard to act like a powered hub.
Of course, this only works with a computer designed for it (with the logic to distinguish a directly-connected "powered" hub device from everything else, plus the electrical connections to supply the additional power to the port when so desired). Which is: the new iMacs.