Earlier quoted context omitted.
It's mostly a fairly recent trend even in the US. For most of my career, I had separate vacation and sick days (as well as, possibly, personal/floating holidays). I'm not sure when the shift occurred but apparently a combined pool is pretty much the norm these days.
The new trend is 'unlimited' vacation days, where nothing can impact you vacation time, because you have to fight with your manager for it.
I would not want to be in a situation where my vacation time depended on some prevailing sense among coworkers of the appropriate number of days to take off.