This is common the world over:
I have yet to sell any permanent storage device ever. usually they just end up breaking, or recycled into a computer for the kids etc.
Though we shouldn't *just* think of residual storage issues when disposing or selling devices.. there's the active lifecycle to consider too, usb drives are prone to being lost, laptops prone to being stolen etc..
Ultimately an education campain needs to be aimed *everywhere* because unfortunately we're not all in control of our own private data.