I wondered about that, too...
What happens if it's running on battery when it starts, the batteries go flat part way through, & the device is left stuck as a result?
Is the only fix^ to be damned-sure to plug it in overnight so any such updates are less likely to get interrupted?
^Fix for Windows, rather than just nuking the device & installing something less wobbly like, say, a one legged drunken pirate on a pogo stick? =-)p