John,
I have only had forms filled out in four shops.
A handbag shop in Florence and Furla's in Rome where I had to request the forms, and in those I had to fill in my details myself.
but, at Capuano (in Rome) and the jewelers in Venice, they just filled them out for me.I have a feeling,
( esp. at Capuano) that is just a service they do , because of the "quality" of the shop.I would think if I made a purchase at Bulgari, or such , they would do the same thing.

As far as doing the VAT in Heathrow, instead of upon leaving Rome,
all I know is I when I stopped at the desk at FCO and they ;looked at my ticket and saw I was changing planes in London, they told me I could not get the form stamped till I left for the States from my final destination.
This was in 2003.
Previously I had always flown non-stop from Rome, so I can not tell you if it is new or not.