Nitpick: tipping is not outrageous in Japan, it’s just politely but firmly declined. Taxi’s are the one exception I know of. The drivers may not expect it, but it’s always welcome. Usually just rounding up.
I remember the episode of Leave It to Beaver where the Beav has to take a cab home, and the driver gets huffy when the tip is only a nickel. Beaver shames him for trying to “take free money away from a kid.” That was broadcast in 1959.
I also remember Fred Astaire playing a con artist in The Towering Inferno (1974), and the first indication that he’s not an above-board guy is when he stiffs a cabdriver.
It’s funny that the OP talks about tipping bus drivers. I wouldn’t tip a city bus driver, but the driver of an airport shuttle usually gets a tip from me. That’s … sort of a bus.
It was a thing in Harry Chapin’s song Taxi (Chapin had driven a cab before becoming a performer) when Sue said, “Harry, keep the change.”
I think it has been ubiquitous in the USA since the beginning of the cab industry, it certainly is in novels set in the depression and going forward. Of course, spy novels and detective novels aren’t textbooks, but it’s a common enough plot point
In Australia.
You may tip your cab driver: you have permission to do so. You will probably let the driver ‘keep the change’ even if you are not an American Tourist. But your kids (on their own money), will certainly expect to be given change.
In Shanghai, I was amazed that the driver casually and without prompting gave change. After driving from the airport to the hotel. I wasn’t expecting that from an Airport ride. In every country, I expect airports to attract the criminal element of drivers.
Singapore. I lived in Indonesia for 17 years, where you tip everybody. I didn’t mind much, but I must say that my frequent trips to Singapore were kind of a nice break - for a few days I didn’t have to constantly monitor my wallet to be sure I had the appropriate denominations of cash to hand out for just about every service interaction.
How exactly is, ‘you’ll probably let the driver keep the change’, anything but tipping?
Tipping less, isn’t the same as NOT tipping.
I’ve tipped every cab driver I’ve had in Singapore, just a couple of dollars, but it’s still tipping.
If it’s an even amount like $20, they get nothin’.
Israel.
I mean, they’ll take a tip if you offer one - if you wanna give away your money, that’s your problem - but it’s not expected.
Uh, always? 
Have you never used a cab before?
How exactly is " But your kids (on their own money), will certainly expect to be given change." tipping?
Your kids getting change is clearly NOT tipping, of course.
But that doesn’t change that the times when you say, ‘keep the change’, it pretty clearly is tipping. What else could you call it? Its tipping by every definition, I’m pretty sure.
About the only sort of bus driver I don’t tip is a city bus driver. Airport/hotel shuttle drivers get tipped, chartered bus drivers get tipped, tour bus drivers get tipped.
Kind of depends what “keep the change” actually means. If the bill is $18 and you pay with a $20 and say “keep the change”, that’s a tip. If the bill comes to $19.45 and you pay with a $20 and say “keep the change” , that’s not a tip so much as you don’t want to be bothered with 55 cents in change
You’re right of course: it is the norm for wealthy American expatriates in Australia to tip 20c + on $75 taxi fares.
(My apology to several other posts that I didn’t include.)
When I was a kid in the 1950s, my paternal grandfather told me that when he took a taxi he would ask in a naive voice, “Do people still tip cab drivers?” They would assure him that it was still done.
Tipping drivers is a norm. I’m wondering when we went to tipping Subway employees…though I feel like a douche for even having that thought out loud. Service workers need the money, clearly.
Tipping in the US was loudly denounced when it started to become the norm in the years after the Civil War, but yeah, it had become pretty firmly established by the early 20th century.
(Emphasis added to highlight relevance to the OP.)
My entire life, and I’m 61. And I drove a yellow cab in NYC back in the early 80s.
We didn’t… That’s not a thing. Sure you can drop your coins in a jar if you want to but that’s not tipping as it’s used for cab drivers and waiters.