I am pretty sure that in theory, anything that might become a projectile during an accident is supposed to be secured. I would imagine that in the event of a late aborted takeoff and runway overrun, most folks' instinct would be to try to protect themselves, and not to reflexively clutch a 5 pound laptop. And should the plane hit something solid at 40mph, for example, it is likely that the majority of the passengers would get away with minor injuries. Except the guy who gets hit in the back of the head with that laptop, which is going to exert 267.5 foot pounds of force on the next thing it comes in contact with.

That said, I suspect that in practice, this amounts to rearranging the deck chairs on the Titanic - but there is also the concept of "control what you can control", so that you have fewer variables to deal with when the poop hits the fan.