I'm not Heathrow but UK and ex HK atc.
The mention of type on arrival is common to other units.It's because many operators do change types on routes without telling us.One operator I can think of has aircraft with different vortex categories.Another swaps Dash8 D with Emb145.Can catch you out if you're busy.Same goes on delivery frequency.
As for giving SID on departure.Yes this is double check,to make sure that you are on the correct routing.It also is a cross check against levels busts.
I'm interested if it's the same at Manchester.It's similar at other Nats units.Just some of their hot topics at the moment.