This trend is confirmed by most if not all sources, also shown elsewhere in this forum.
I think however, that if the trend is correctly reflected, there are always doubts regarding actual transactional process. I read an interview regarding another car make, that in most cases the prices taken in consideration were asked prices as presented by sellers in their announcements. However, when you look at the three posts that are currently offering two 250 and one 230, the levels are more or less matching the graph.
As a side observation, I am quite surprised that the graph shows a steady increase in the period 2008-2011, which were the years of the economic downturn or even crisis in some countries. From what I noticed, prices were much more elastic than what the table shows. I bought my car in the US, but my shopping covered primarily Europe and my recollection is that 230 could be sourced at lower prices than that (to avoid any doubt, I am not speaking about the so called project cars, but rather about a car in good or very good condition).
Today, if we take a car sold by Brabus and another one out of those offered on our website, the graph will show an average of roughly 125 th Euro.