I think AF and KLM are in the same group. Why do results seem to differ so much between the 2 of them, it cannot only come down to cultural differences
You can attribute a lot of the difference to culture. There are some shallow aspects, like "what's the best beverage to drink with lunch?" and the language issue is also one of the more shallow ones. Where government in the Netherlands is encouraging students to learn foreign languages (in particular English), France is more concerned with supporting the French culture and language.
The big cultural difference (with a great impact on CRM) is that the Dutch (especially in the area around Amsterdam) are quite anti-authoritarian. A manager who just orders his subordinates around will be asked to motivate his decisions pretty soon. On the other hand, people on the work floor are not shy to warn when something threatens to go wrong. As preventive action managers schedule "meetings" where people can spout their issues so the manager can deal with them before they become problems.
The French culture is more one of respect for authority and good relations with the people around you. Potentially angering a colleague by saying he did something wrong is bad for the relationship. Don't dare to offend your chef! So problems often tend to simmer, unless someone finds out, leading to a French-style vocal explosion. It might require a common trip to a tavern to mend the damage to the relation over a few glasses of wine.