But in other countries in that region (say, Poland, Belgium or the Netherlands) you'll find a completely different culture.
In Germany for instance in many firms even today it is still very customary to indicate a senior in the company with 'Sie', the polite form 'du' would be frowned upon unless it has been explicitly stated that that is permitted.
I seriously wonder how much of the report should simply be viewed through a German cultural lens in the region where the research was conducted, instead of used as a universal set of truths regarding humour the way the article suggests.
You really have to keep in mind that Germany is still very 'status conscious' compared to many other countries (at least, in my own limited experience, maybe 50 or so trips into Germany visiting people and businesses for various reasons).
But the article's subtitle is something that does seem pretty spot on - and makes you think a bit:
"telling jokes is a method of reinforcing a social hierarchy"
And as erlanger's comment says - the end of the article crystallizes the meaning pretty well:
"Nurses and midwives tend to tell jokes about patients but not when the doctor is present. And when someone initiates a joke they tend to be ignored if they are in the presence of someone of a higher status."