I had a colleague fly through Amman last night. They had him remove 100% of everything from his briefcase and checked everything for bomb residue. If I had to guess, the US has intelligence that someone is going to bring a bomb (or some other weapon) on board a plane using a Laptop Form factor. I'm also guessing that the type of damage one can do with a device in the Cabin is greater than that can be done in the luggage hold (which is why the Laptop can be checked, but not brought through carry on.)

Though, I'm open to the alternative theory that having people place their laptops in checked luggage gives them greater opportunity to do targeted surveillance without their target being aware.