Granny - I never mentioned taxi drivers? It was MrsWinnebago who said that her criteria for tipping was whether she had received a personal service.
I personally think that giving a gift to people (like care workers, or teachers) is very different to tipping. Firstly from a purely financial viewpoint - a one off bottle of wine or flowers once a year is a very different outlay (and income, to those receiving) to paying an extra 10-20% on every meal, taxi ride, haircut, manicure, massage, etc you ever have.
Secondly, tipping is historically a relic based on inequality. The rich would always tip the poor for performing a service well for them. There is still an element of this in tipping - the served are assessing the server, and deciding how much they are 'worth'. The fact that tipping is always monetary reinforces this. But giving a nice present, appropriate to the individual, to someone who you have developed a relationship with (not a random who you takes your order, delivers your food, and spends 5 mins max with you), at a 'recognised' present exchanging time, like Christmas, retirement, etc, is a much more equal concept, and a much nicer way of recognising someone's hard work, I feel.
You say that it is nothing to do with salary - but of course it is! You wouldn't tip your doctor, or lawyer, or consultant, would you? No matter how exceptional (or personal) a service they had performed for you?