The fundamental difference is that if Joe Public thinks there may be a safety issue with getting on a train, he won't, and Virgin lose money, shareholders get all upset. When one of HM's airframes becomes the first to arrive at the scene of the accident, other than a prompt determination that there is not an overriding safety issue with the fleet, it is business as usual without the commercial concerns that Branson has to deal with. Service personal don't have the luxury of a reassuring message from some senior nebby that all is well.
Also, despite all the best
PR spin in the world, Virgin do not know exactly what happened yet, they have made an educated assessment and understand the key facts behind the accident, but it will be some time before they know exactly why it happened. Just following basic accident investigation procedures is a time consuming and intensive task and it always will be regardless of the public's "right" to know what happened immediately.
As impressive at it may be, don't forget that this openess is simply driven by profit - not concern, and that's the difference between this and Military accidents.