> Operating systems kind of suck at it.

Sure, but they usually have more resources than programming language teams. Consider all the programming languages on your machine. Can you trust they all did the timezone, with all its nuances, correctly?

Consider something simpler - the trig functions. I've noticed time after time that many language libraries get it wrong, and this is with decades of development. Errors are usually in the form of precision that is lower than it should be, and poor handling of special values like NaN and infinity.

The situation with that is so erratic that with the D programming language we'd write our own trig implementations rather than use the C library ones.