Audi has seriously upped its game over the past 3 to 4yrs and addressed any weakness it has against BMW the class leader in the small exec saloon market. Particularly they've improved the dead feel of the driving experience and combined with their Quattro option look to be surpasssing BMW standards.
The other factor is design. While BMW have prevaricated over the controversial Bangle design era and failed to send him home to California. Audi have struck and overtaken BM on interior design and match BM on exteriors.
Will this 2ltr TDi match BMW's silky uber-efficient diesels? I recently hired a 1.9ltr TDi and from the French coast to Paris and back (600+ miles) it cost a paltry £65 to fuel. Amazing!