More likely, crap hardware, which is awfully hard to avoid in USB-land.
Just the other day, I traced a machine that failed to reboot to an external USB disk. Unplug it, machine boots right up. Move the same disk to a machine as different as can be — different hardware, different OS, different firmware… — and it kernel panic’d that box within about a minute of plugging it in.
Then there was the time a USB enclosure ate my data. Only the filesystem’s strong checksums saved me that time. I moved the disk to another enclosure, and the bad sector writes stopped occurring; all else remained the same.
The problem is a market conditioned to believe that it should expect to pay $13.64 for an enclosure, power supply, and interface cable and get a 5-star product. If you put a $200 enclosure in front of the vast majority of members of that market, they’d either disbelieve the price or rate it 1 star for bad value, even if it was guaranteed to outlast the prevalence of the USB standard it supports, had a higher transfer rate, and had guaranteed data corruption rates best given in scientific notation with large negative exponents.
Whenever I have a machine with an unkillable userspace program, I run dtrace, and almost always get told exactly which bit of hardware (and therefore which kernel driver) is holding the machine hostage.
You might be able to dig the same info out of /var/log/messages, given close-enough timestamps.