Historian: The standard "QWERTY" configuration of the keys on typewriters and computer keyboards was originally desig...

I think the key word in the stimulus, "frequently" hints at why the necessary assumption in E is fine to make. While it is probably true that keys on a keyboard for a computer jam, it certainly doesn't happen frequently. I think the word "frequently" in the stimulus is giving the LSAT takers as much common sense leash as they can give.