I actually don't see the difference between tips and non contractual bonuses, except perhaps one of magnitude. Each tend to be accompanied by threat to withdraw services if not granted.

Do you tip in restaurants, and does this change if the bill already includes a mark up for serve automatically? What about taxi drivers, hairdressers etc?

I remember when I was a relief postie back in the day. Only did one or two weeks at Christmas, but got more in "Christmas boxes" in those two weeks than I did in wages. I suspect the regular postie's who had worked the other 50 weeks to generate these tips were not impressed.

I take your point that in your world recognition was "non financial", same is probably true in the NHS, but whilst both are large employers, I suspect they are in the minority as regards incentivisation patterns to remuneration.... especially if you throw in share option schemes which are now very prevalent.