Actually the satellites don''t even belong to Sky, they're rented IIRC (or rather many of the transponders pointing at the UK are), from memory Sky don't actually have many/any physical assets pretty much everything is leased to reduce the risk to them (if the satellite gets damaged Sky don't have to worry about funding a new one, they just rent space on another one if possible).
You tend to pay Sky to be included in the EPG, the cost of transponder space is up to the broadcaster to sort out, as is the uplink from memory.
From memory Sky actually make it quite hard for broadcasters to use the same satellite as them under certain conditions, and charge extra if the broadcaster wants to be on their EPG but in an unencrypted format (IE the likes of the BBC which are on Freesat unencrypted have to pay extra).