An USB hard disk could have partitions, NTFS, FAT12,16,32, or 'other' partitions and just too many variables for it to just work for a consumer market. Let's define that for a consumer product you can't survive support calls.
I have seen a few read USB 1GB memory sticks which is pretty cool.
my son just bought one, it reads every format under the sun, and also has a card reader and a USB connection...
the USB will read his camera RAM but then he asked me "why won't it read an external HD with mp3s, pics, and movies?"
i said "ummmmmmm because?"
is it possible?