are you suggesting the cars didn't need good brakes
I am suggesting that, as you quite rightly say, modern cars do indeed have much better brakes however, today's drivers exploit those superior brakes by driving far closer and preforming far more dangerous manoeuvres, than was previously the case. This somewhat cancels out the benefit of better brakes.
And for the record, I support varying speed limits - clearly 70 mph in dry conditions on an empty motorway is too lower a max speed limit. Likewise, 70 mph in wet conditions on a crowded motorway is too fast.
Rather than speed cameras on motorways, I would like to see cameras which clock those who drive too close to the car in front - the technology for that must exist. You would probably need several cameras (3 maybe ?) over a short distance (100 metres ?) to allow for the tossers who pull in front of others. Not only would these cameras dramatically reduce the amount of accidents on motorways - and, the amount of vehicles involved in each accident, but they would also allow traffic to travel smoother, and therefore faster..... God I hate the 'foot-brake touchers'.