Whether the employers tolerate it or not doesn't seem to make much difference. I don't see any evidence that it is heavily enforced. There's plenty of people using the internet heavily during work hours.
Also, not everyone is in fact working during work hours - students, part-timers, people staying at home, etc. all contribute to working hours being the most active online. To say that "private people search in the evening" just does not ring true at all.