Do you know for a fact that they do develop their software in a waterfall like method? I somehow doubt that a bit. At least they publicly say:
"Volkswagen Group IT consistently uses agile workstyles and intensive cooperation with universities, technology partners and Volkswagen Group departments to develop digital solutions."
"Volkswagen Group IT consistently uses agile workstyles and intensive cooperation with universities, technology partners and Volkswagen Group departments to develop digital solutions."
http://www.volkswagenag.com/content/vwcorp/info_center/en/ne...
Of course, cars do have a lot of legacy (not least because of inertia caused by regulatory processes) but I think they do a bit of what they say.