Dr Wendelin Wiedeking must have been bursting to explain the Porsche investment in VW for ages. All those months ago, when the announcement was first made and the conspiracy theories were thick on the ground, there was very little guidance as to why on earth a small, successful, independent, sports-car company would want to be heavily exposed to the vagaries of a volume car company saddled with an arcane shareholder structure and with an obsolete trade union power block on the governing body.