Actually, that's not how it works. There is no requirement to drive at the speed limit.
I never said it did, but someone driving is such a way clearly shows a reluctance to drive faster, which is down to lack of confidence. People who lack confidence makes mistakes, this translates in to a danger for themselves and other road users. Speed does not translate into danger if the laws and guidelines are followed. You're little Trusim about a man crashing is an idiot, well he's an idiot if he crashed at 59mph too. There's no defence for driving too fast for the conditions.
As Raymond has said this was an A road in which an articulated lorry was being held up by a car being driven too slowly for the conditions. Driving in such a way without the ability to be overtaken is discourteous and will lead to drivers performing unsafe overtakes through frustration. You will incur marks against you if you on your driving test do not 'Get up-to the speed of the road quickly' - so if an articulated lorry is being held up how is she not up-to the speed of the road? Traffic Police will also take a dim view of people driving in such a manner.
I don't agree with defending the race to the bottom of driving standards, they should be constantly challenged to be higher than they were as that's the best way of improving road safety, not just saying 'stick below the limits and it'll be all roses'.