I think I am reluctantly going to have to disagree Den. It has been reported in the past that Sky used underhand tactics to destroy competitors (as Sirius points out i.e. the cards for itv digital.)
I doubt Sky will dare to try anything like that these days, with their current reputation as it is, and by having been found out by Panorama.
They complained about BT nabbing the rugby rights off them, but afaik, nothing came of that complaint and BT still have the rights.
I will be interested when the ECB cricket and RFU England international rights come up for sale again. I can see BT either going after them on their own or teaming up with one of the free to air broadcasters to try win the rights.
The only thing I see Sky having in their armoury now is vast, vast sums of money. If they spend too much money (which they will, the past has taught has this), and pass it on to their customers, I think people will vote with their wallets.
Having said that, I think Sky will continue to win the premiership rights and will continue as a strong channel (due to international sports i.e South Africa/Austrlia cricket/rugby matches etc) but I think BT have the power behind them to stay in it for the long term.