I use to say the same thing, until i drove beside a cop doing 120kph, and even up to 130kph with out them doing anything. (many diff times)
the minute they set it to 120kph or even 140kph, everyone will be doing 160kph…so by keeping it to 100kph usually cops dont mind the extra 20kph because yes, it keeps a good flow on the highway…They can be dicks and pull you over if they want, but they will never unless they need to make some money giving out tickets.
(people keep for getting cops are a paid service by the city, they are no diff than a retail store, they make there own money for there devision by giving tickets too.)