You only really come across supplies like that in fairly far flung villages. I've lived over there and the supplies and installations in modern homes, certainly in urban areas, are perfectly acceptable and to modern standards.
I think a lot of these old places have wiring dating back to the 1930s/40s (i.e. pre WWII!). Many British and Irish tourists end up staying in already converted, or buying and converting old, relatively run down farm out buildings in fairly far flung spots in France.
They do make ideal holiday homes once converted, but I really wouldn't base my opinion of French wiring on what you find in some of these places.
