I guess it's a result of a hundred years of slowly gained privileges getting added on top of each other, and bureaucratic rules muddling everything up every decade or so.

In Sweden, you accrue vacation pay as you work, and when you take your vacation, it's paid out and because of some law or other, it's larger than your regular monthly paycheck. So in essence you get a little bonus for having your paid vacation, same as a bunch of other countries that people have brought up in this thread.

However, if you're paid by the hour, it works exactly like you suggest. You don't accrue vacation pay or vacation days, and x% of your hourly pay is the included extra vacation pay which you just get straight up.

When you negotiate a monthly salary, the number is without the extra vacation pay, but when you negotiate an hourly salary it's with the extra vacation pay. Because, it's just the way it is. :-)

Well, that's more or less how it works. The vacation bonus of 8% percent of your salary is reserved each month, it's just common to pay out at the start of the summer.

But paying out once a year is the legal minimum, you can agree otherwise. At my previous job, we switched to twice a year at the request of the snowboarders that needed the money for the winter vacation...