1) Discovery group has a seperate agreement with VM on carriage of its channels. The HD versions are fed direct to VM's main headend, so it would be simple to add the SD versions currently recieved via the Sky (Astra) satellites.
2) The channels are owned by Liberty Media, part of the same group as VM's owners (Liberty Global).
I have got to say, the likelyhood is it will not happen. We have been here many times before with Sky having disputes with channels. If there is a "Blackout" on Sky it does not normally last long. Virgin have done this with the Sky channels in the past. As you say, Sky would lose a lot of viewers if they were to do this.
Cable customer since 1993. Services: FH TV, Sky Sports & Movies (2xV6), Talk Anytime Phone, VIVID 350, Virgin PAYG Mobile