Airlines like Delta and British Airways recently started allowing passengers to use tablets and smartphones during takeoffs and landings, yet they still restrict the use of laptops to within the air only. Is there a justifiable reason for this (i.e. safety; regulations), or is this policy just arbitrarily chosen?
The Expanded use of the Portable Electronic Devices (PEDs) was initiated by FAA a few weeks ago. The decision was made by a group of experts from FAA, airlines, manufacturers, pilots and cabin crew.
This expanded use allow passengers to use their devices at all times (from gate to gate) with little restrictions. Including:
You can also read FAA's press release regarding the expanded use of PEDs for more details.
I would say this is mostly for safety reasons. The EASA states the following:
So in short it's to prevent laptops from flying around (them being a lot heavier than mobile phones or tablets). And the other reason is that it doesn't hinder you from getting out fast of the plane when necessary.