But I've also installed Honeywell in mansions and granny flats alike, so I still don't get your point that the Horse of the Year Show Set pay for better heating brands than the rest.
Honeywell made the aquatrol 2000. I don't think you would fit that in a granny flat. Not sure what the successor is.
Doitalls projects will have involved dedicated control engineers who I don't think would waste their time fitting say two channel salus programmers in granny flats.