Originally Posted by
CPMaverick
The reason behind it is the same reason that all carry-ons must be beneath the seat or overhead- projectiles during turbulance.
Though some laptops are quite light, others are heavy and could fly out / cause injury in severe turbulence.
Highly unlikely I know... but I believe that's the reason behind the rule.
On such a long flight... I don't think your seatmate would be that bothered by getting up twice.
This is what I've also been informed as well. I've also heard it implied that the purpose of the seatback pocket was for placement of the emergency procedures card. Another version mentioned something about the airline only allows the items they place there (i.e., emergency card, convenience bag, magazines).