Spotwelder might be able to confirm this however I think one reason few airlines, including BA, don't offer Channel 9 is that they fly to countries which don't permit listening to air traffic control broadcasts.

In the UK it is iffy on legal grounds from what I can tell. Although I am not entirely sure.

What with BA's vast route network, their aircraft can end up practically anywhere, more so than UA's aircraft which tend to me more Far east, western Europe and Americas based. i.e: the 'safer' parts of the world.