It's starting to look as though the real problem is legislators allowing (or insisting upon) vehicle emissions tests that bear no resemblance to normal use. The same must be true for all vehicles, not only diesels.
It's inevitably easier to build a car that can comply with clearly defined special circumstances such as a laboratory or a 'poke this up the exhaust and rev the engine' stationary test, than it is to make the same car meet a given standard when it's being driven on real roads in real weather with real loads by an average driver - but it's also a lot harder to test the car in the latter circumstances. No cheating required (so it is surprising that any major car maker has confessed to cheating). This must be true for all cars, not just diesels.
It has been widely known for years, I think, that when cars are tested in the real world the results bear little resemblance to what can be achieved in a statutory annual road worthiness test - let alone the original manufacturers lab tests. It may be that the statutory emissions limits are not actually achievable in the real world, at least not without making the cars a lot more sluggish to drive. This too applies to all internal combustion cars, not only diesels. It also calls into question the principle of differential annual taxation based on the OEM figures, as practiced in the UK.