I think that concentrating on flights from specific airports suggests that they think the security checks at those airports are insufficient. Anyone who does a fair bit of international travel will be aware of the differences in security checks.
There's also the question of how much safer, if any, it is to put the devices into checked-in luggage.
http://www.bbc.com/news/uk-39343971
See the discussion here
https://www.bloomberg.com/politics/a...-force-changes