Every time Google or Yahoo close down a product, they should have the team lead explain what happened in a video. It would soften the blow to the community and give a nice face to what often seems like a harsh move.
Which leads me onto your second point - that's exactly the reason Yahoo or Google don't do a video when they shutter a servie. They have no intention of telling you the real reason for shutting a service down (eg "it wasn't making enough money", "it's not strategically important any more") and if they gave a BS video we would all know it.
Which leaves me to conclude if you are not going to be straight forward about why you a closing a service (the rights or wrongs of that are beyond scope for here) then perhaps it is best to say little/nothing in a nondescript blog post or press release - and certainly not a video.