First of all, please note that Rolex is not a German company and therefore should not be used to make any generalizations about Germany's culture.
The other companies, and especially the two auto companies, are known for the high quality of goods that they make. This is said to reflect on Germany's culture. People see Germany as a country in which people are very good at being well-organized and in which they are very meticulous about doing everything right. This is reflected in the fact that Mercedes and BMW have a reputation for being very well-engineered cars that are also very high quality. Ads for these cars tend to emphasize "German engineering" because high quality is seen as a typically German trait.
Overall, then, the German companies on this list (you can argue) reflect the fact that Germans are inclined to want to do things with precision and care. This is how Germans are seen by many outsiders, partly because of these companies.