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."

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.