That depends of the country and its regulation. I get pay extra for my week as oncall, plus a bit for each page outside of working hours. As for the oncall responsabilities, we take it as time to catch up on debt or open tickets, no project work is assigned that week.
There are limits on working hours, but I guess the reason is obvious as elsewhere.
You have your team of 20+ developers/sysadmins working Mon-Fri, 9am-5pm, and then you have a single individual responding to on-call events outside those hours.
Assume an average rate of €10/hour, with a working week of 37.5 hours, that gives you an income of €375.
If you're working 7.5 hours a day, you're on-call for 16.5 hours Mon-Fri, and 24 hours for Sat/Sun. That gives a total of (( 16.55 + 48 ) 10) = €1350.
So yes, you get paid a lot. (Of course the hourly salary there was low to simplify the numbers, but you can see the income for working a week on-call is about the same as working three normal weeks.)
