I think that the real root of the problem is that these tests are done in a lab rather than out on a road. It shouldn't be beyond the wit of man to contrive a "standard" section of real road (i.e, no gradient, same surface and camber etc) on which all cars can be tested at a number of different road speeds. There are already portable gas analysers out there which can be connected to the exhaust of a moving car; I watched a video of one on the BBC News website just yesterday. As for other manufacturers cheating in the same way, I would be frankly amazed if they weren't all at it to some degree; it's too tempting.
I stopped buying diesels only because I wanted a particular model of car and the local dealer had an ex-demo one at a very good price - but it was a petrol-engined model. These days I only do a fraction of the mileage I used to do when at work, so the fuel consumption isn't that important. As for emissions, I have a problem when comparing those of a 2-litre diesel car with a forty-foot articulated HGV. Incidentally, both my car and Elizabeth's are supposed to do a combined MPG of over 50, yet neither of us can get more than 36.
You're daft if you believe a car salesman's blarney, so why have any more faith in the car manufacturer? Capitalism has made cynics of us all.
Dave M