The US is the only country I know of that demands income taxes from its citizens when they are non-resident. Citizens of most countries would expect to pay local income taxes only when they emigrate.
Although it is important to remember that any tax one would have to pay to US IRS is for the difference between what a foreign country and US would charge, if former charged less. This only applies to countries with which US signed a treaty for the avoidance of double taxation.
I'll note Canada has a similar treaty with the US and this applied to me while working / living there for a number of years.
They wanted to tax me on my "worldwide" income and requested that I pay the difference between what I was making in the US vs. what I would be paying in Canada had I been living there.
It wasn't something I had considered in my planning so good to look into before you go!
Interesting - from this and a couple of other comments I can see my idea that you just had to pay US income tax regardless was over-simplified and wrong.
It's still a little weird to me though, as someone who would expect my own country to relinquish all tax demands if I'm not actually there!