I was speaking to an ex-Lotus engineer recently.
With a regular churn of engineers among the main car manufacturers, it is apparently common knowledge on the inside that all makes adjust their emissions according to whether they are being tested. It is part of what their engine management systems do anyway (adjust to the conditions). A bit like MPs expenses, there is some bewildement that this has created such a storm when it was just considered "one of those things that everyone else does, so we should too".
I think the main issue for me is how far out of kilter the VW test and real-world emissions were, not that it was being done at all. You can bet your life they all do it to some extent.