Possibly less mileage due to recession. Also ... there was more awareness of danger and less reliance on gadgets...
Worryingly - our guys have pulled more reps and HGV drivers thinking they were were impaired from illegal substance. Turned out they were "tired"
Longer distances, more "monotony as drive takes longer"

amongst the excuses. A lot, in fact, claim that ABS, air bags, crumple zones protect

Perhaps the gadgets have led to certain amount of complacency
They do protect .... to a certain extent ... but not in Cinderalla's fairy godmother terms

You have to know how to use the safety gadgets and be aware of their limitations.
We have logged all the excuses for records and analyses ... but still prosecuted for undue cares, speeding etc.
(And some of you will no doubt ask me "How can we!!! How can I condone this! Unfair!")
Well ... take the view that driver is "manager" and as such should be able to judge whether or not he or she feels fit enought o handle machinery which is quite capable of harming themselves or another person in real terms ... and we have an obligation to protect people from themselves under those circumstances.
However, am prepared to acknowledge that an inappropriately low speed limit can increase danger - from fatigue and can alos cause concentration to wander.
Most of you know that we do apply common sense in reality

which does depend very much on circumstance and attitude
V8 Archie ... cannot really answer your question (nor the other one about the SIs -- Mad Doc is perhaps better equipped for that one).
But it is certainly food for some speculation. I have tried to give you pointers from my side - as I have seen and assessed the increases.
I also think that the reduction in my number, over reliance of road safety on a camera, decline of road safety adverts have also impacted on behaviur and knowledge of the Highway Code over this same period of time ... all of which picked up on in Paul's manifesto.
Just my initial two pennorth worth of thought