RC:
 

... The US EPA already announced they would check software from other Diesel car manufacturers as well and in Germany, the scandal just started, the responsible authority KBA will do the same but the government may not want to make a big fuss out of this because it could harm the German export industry. ...

The researchers who discovered the discrepancy with VW/Audi also tested a BMW (I forget which model) as part of the project they were working on (to show how clean clean diesel is today) and it did not exhibit any unusual behavior. That's not to say that all BMW engines are "good", they may well be

So far, it's only this one engine that VW/Audi cheated with, I'm guessing because, pretty far into development, they realized they were never going to achieve the performance and/or fuel economy and/or no AdBlue goals and meet the emissions requirements, and someone decided to go with this cheat rather than scrap the engine development. Has this happened in other cases? We'll find out, but it could be an isolated incident.

However, if I were the EPA, I'd focus first on engines that seem to "have it all".