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The "right" way to do this is a thermostatic mixing valve at the water heater output. This lets you keep the tank at 150°F (or whatever) but the output gets mixed down to 120°F (or whatever). It also gives you an effectively-larger tank which can be very useful in certain cases.

Of course, you might say, why not put the thermostatic mixing valve at or in the shower, which also works pretty well!

Interesting. On the other hand, when bringing a newborn home from the hospital, the take-home literature instructs new parents to turn the water heater down to 120 F to prevent risk of scalding.

I wouldn't worry about it. Almost every modern boiler will bump up the temperature to 60C / 140F once a week to prevent Legionnaire's, may even be a mandatory feature depending on where you live.

> the 20–50 °C (68–122 °F) range

That's clearly a case of conversion results being given unwarranted precision.