I haven't had an opportunity to read all of your topics , however thought I would mention..
Disc Saws are used in a large number of operations over here , including Ventilation more than anything.(Opening roofs, creating vents in the tops of structures etc) Followed secondly by allowing the truckies access to doors. (commonly rollerdoors, factory doors, secured buildings, anything which cannot easily be popped with a Halligan Bar, Sledge Mallet etc). I have not seen a disc saw used on a Vehicle incident.
Regarding what this equipment is stowed on, we do carry them on Rescue apparatus, however most commonly they will be used by a truck crew,(Known as a Ladder crew also), it would be rare that a Rescue apparatus arrived on scene prior to a Ladder.