I'm not certain from my read of this; are Dyson saying that the cleaners submitted for test were deliberately set in low power mode regardless of dust levels (i.e. special test samples), or are they saying that the standard test does not include any dirt and therefore they were correctly running in a lower power mode?
Case 1 seems utterly wrong, case 2 seems fair enough to me.
Obviously I am not a vacuum cleaner expert though, but my job does suck if that counts...