You may be right, BS. Thinking back, I had an internal flight in the US, no upgrade. And no upgrade on the flight home either. But neither of these airports had facilities to use the watch for check-in. So analysing these statistics...
Checkin using Apple Watch, 100% flights sampled
instantly offered upgrade to Business.
Checkin without Apple Watch, 0% offered upgrade.
I guess that's pretty convincing then?
BTW, watch-related or not, I could get used to the lounge at Heathrow. Comfy seats and a help-yourself bar, with a decent range of single malts... Not a bad place to kill time before a flight. Oops, spot the pun.