Here am I about to agree with Old Boy here.
Back in the day Setanta joined XL TV and it was widely thought something in the region of around £2.50 per XL TV (equivalent) went towards it. The logic to Setanta at the time being Virgin subscribers are less likely than Sky subscribers to buy it standalone at £12.99 or whatever it was.
There’s never been a “one off” increase as a result of changing to ESPN then BT included, it’s simply been absorbed into the overall price. The point that japitts raises is a good one above - if a few hundred thousand subscribers who do watch BT and have Ultimate Oomph coughing up £100+ a month moved to Sky suddenly the fixed costs (network upgrades and maintenance, interest payments, etc.) are having to be met by a smaller subscriber base and a sizeable amount of income removed.