I think that, as noted in the RoSPA advice, that will ultimately generate more wear on the gearbox than simply waiting in 'D'.
Just as in a manual the hand-parking brake should be set whenever you are stantionary for longer than the time that it takes to comfortably set it and release it. This will vary according to circumstances, including the vehicle.
Sounds perfectly logical and reasonable. See above.
I suspect that's more likely to be because those people are driving manual cars and simply cannot be arsed to use the handbrake.
Labouring? I don't think so. Certainly the engine idles a few rpm lower but I would hardly call that labouring.
I sincerely hope not. Pbutt or fail should be based on safety and vehicle sympathy. If you can be economical whilst doing so then so much the better but once "saving a couple of drops of petrol" becomes a key concern then that really is the beginning of the end.
-- Mark Foster, Brighton, Suslove, UK PGP Fingerprint: 3342 C02C 7BE8 3FE4 AAC5 8BB2 03B7 9263 DDF2 04C1 -------------------------------------------------- "There are no such useless words as, 'I didn't have a chance.'" Driving, HMSO