I'm not that impressed by the testing procedures.
For example, apart from he MOT test which is just while idling I believe, there is no testing of older vehicles. So if performance totally drops off after 10k miles, we will never know.
I'm pretty sure that BMW hid a problem with the VANOS that would most definitely have severely affected emissions (and performance). There used to be a warning thrown when the VANOS wasn't operating properly, but the warning disappeared, together with some improvement in engine behaviour when the VANOS didn't work properly (i.e the engine management switched to maps for this particular case).
Of course, this VANOS problem never showed up on any new cars. Only after 20-40k miles did it show up.