I can fix it!
Sounds like a common problem with USB ports. On Windows computers, there's an option for USB ports to automatically shut off after a period of time to conserve power, especially on laptops. If that interrupts the update (which must be a pretty long update for that to interrupt the connection, I might add), it would logically cause an error. All people need to do is make sure their USB ports aren't set to shut off for power conservation.
Start > Settings** > Control Panel > System** > Hardware** > Device Manager > Universal Serial Bus Controllers > Right-click USB Root Hub > Properties > Power Management
**For Windows XP and earlier only
Too bad Apple's not familiar enough with Windows to warn its customers about this all too common issue.