The same magazine that quoted an average price of 25 Euros a night for a pitch in Germany and 34 Euros in France lists an average price of 41 Euros in Italy, making that, according to them, the most expensive (on average) country for caravanning in the whole of Europe. I can't confirm those figures, but I have no reason to suppose that they are way off the mark.
I think that you were just unlucky regarding the inability to communicate in English, or else you only dealt with older people who didn't have English as a compulsory foreign language at school, as is the case today. You mentioned Colditz which is, of course, in eastern Germany, where Russian was the main foreign language until the early 90's. One would definitely have less of a problem in the west.
As you correctly state, Aldi and Lidl, while widely prevalent even in the smallest towns, generally have relatively modest floor space. However, other chains, like Real, Toom, Globus, etc. can be compared much more closely with the French hypermarchés for size and their prices compete with Aldi and Lidl.
Petrol prices in Germany are very volatile. They go up and down like a yoyo by as much as 8 Eurocent a litre, sometimes even during the course of a day, so it is perfectly possible that France is cheaper at certain times, but this can equally be the other way round, too. Luxemburg is a special case and is always cheaper than all the adjacent countries.
You're statement about a change of rules in Germany suggests that the speed limit was brought down compared to neighbouring countries unless the caravan is specifically approved for 100km/h. In fact, quite the opposite is the case. The speed limit for such caravans was actually raised compared to the 80km/h limit which applies in most countries like The Netherlands, Denmark, Austria, Switzerland, to name just a few. Besides, the speed limit for lorries is 80km/h, too, so there is no reason to be constantly overtaken by them.