@ Steve the Cynic
I completely respect the fact that you have an average vehicle ownership time of "a bit over four years". Obviously, in your particular case, my analysis does indeed fall down.
Now, for my analysis to "fall down" globally, you'd have to decide that most people have the same average ownership time. You will allow me to doubt that, if only for the fact that I know people who change vehicle every two years. In my particular case, I have owned an Open Kadett for 11 years, a BMW 330d for six and a half, and my latest is an Audi A5 which I bought in 2012 and I am nowhere near thinking about selling it. That is among a few other cars that have passed in my hands more briefly, I freely admit. So my average is significantly higher than yours, even considering the Laguna 2 I only had for 3 years.
I will not, however, consider that my ownership times are common either. I base my opinion on the fact that are more poor people that own cars than there are rich ones, and if the rich people do indeed have the means to change cars regularly, poor people don't. Rich people can choose how long they want to own their car(s), poor people make do with theirs until they don't have the choice any more.
I do believe that that tends to bring ownership times to significantly over a presidential mandate. I will be quite happy to be directed to some actual statistics drawn from a population study that demonstrate that this belief is wrong.