Volkswagen's main profit driver - Audi - is suffering from stagnant earnings from slumping demand in its core European markets - where it sells half its cars.br br Audi's operating profit at Audi edged up just 0.6 percent last year to 5.38 billion euros, compared to a 60 percent surge in 2011.br br Net profit fell two percent to 4.35 billion. br br ...