AFAIK Both Sky and BT spread their price increases across all subscribers regardless of what package they are on. I don't know the ratio of spread - I would expect/hope sports subscribers to pay the larger share - but I believe it's spread everywhere to soften the blow.
As the sports channels are optional, but the base package of channels isn't, this prevents the sports channels from becoming off-puttingly priced, as they are by far the most expensive to produce.
Biting the hand that feeds IT
