I have done a lot of intensive and hands on research about road traffic crashes - more than 40 years of it to be exact. It is not the car which is the core element or cause of a road traffic crash - it is the human being in control of that car who is the core element of crashes. How cars were when the standards for current speed limits were set up had virtually nothing to do (in my country at least) with the criteria used to set up the limits - the criteria used was twofold: (1) "human perception time + human reaction time + time taken, after the perception/reaction phase, to complete or achieve what is necessary to avoid an impending collision like stopping or swerving in time". (2) The actions and reactions of road users based on their experience and expectations of what they perceive other road users are usually doing - virtually all driving decisions are based on what the driver expect or belief another road user is doing based on his previous experiences regarding the usual behavior of other road users. Example: when a driver wants to cross a road he looks for approaching vehicles on the road he wants to cross and when he saw a vehicle approaching he will decide, based on his previous experience and what he normally expects from other road users, to cross or wait. If the approaching vehicle is at a distance which his experience taught him he has enough time to safely cross, he start crossing the road. Now imagine, if the approaching vehicle is doing 130 miles per hour instead of the 30 miles per hours it is supposed to do at that section of the road, what would happen? (the point here is that it is not the great capabilities of the driver or the greatly advanced modern car of the speedster that should be the criteria for determining speed limits but the reasonable expectations of the average road user).
The speed limits were thus based on the average time it takes for an average human to perceive/react/achieve in relation to the rate of speed of a moving object AND the way the average road user usually react to the actions of other road users.
It is thus the capabilities and perception of the human which is the central factor in collision avoidance and NOT how good or bad the vehicle is. The modern car may have improved tremendously over the older cars BUT the capabilities and perception of the human (the road user) has NOT improved (changed) at all between then and now so no new justification or reason to change the current speed limits came up.
It is true that poor driving skills, recklessness, negligence and criminal behavior (breaking the law = speeding) are SOME of the factors that must be present to cause an accident but the other factor SPEED (speed is the rate of movement of an object) must ALWAYS be present as without it no collision can happen (no movement = no collision - unless you belief in motionless collisions of course). The test to decide if a factor (speed) is the cause of a result (collision) or not, is to simply take away the factor and see if the result still follow - if the result can not follow without the factor, the factor is obviously the cause for the result. A collision is a forceful contact between two or more objects due to the movement (speed) of one or more of the objects involved in the collision and the force of the contact (lethality) is caused by the rate of speed involved in the contact - so speed is not only an essential cause (requirement) for a collision to happen, it is also the main cause of the severity of the collision AND will determine if the collision can be avoided or not due to to reduced action/reaction time available caused by higher speeds. Today, in contrast to the past when current speed limits were set up, traffic is very much more dense and the typical distance between people/vehicles on the road is much less (much shorter distances) than in the olden times drastically reducing the available time for road users in which to act or react so current speed limits should in the interest of road safety be reduced and not increased. As to your moaning that speed limits make only the government / police department / insurance companies rich I counter with the following: (1) do not make the criminal speedsters who have no regard for the law or the safety of other road users out to be "poor victims" - they are not! (2) The desire to speed in public spaces can not outweigh the desire of the law abiding to be safe on their roads. (3) Speed limits can not be based on how good a driver you are or how fantastic your cars is - it must be based on the capabilities and expectations of the average road user. (4) Speed limits can not be based on your lightning like reflexes or the carbon fiber brakes of your car but on the reflexes and standards of the average driver and car. (5) "Let crime pay" - it cost to protect the law abiding road user and somebody must pay for it. I much prefer that the criminal rather than the law abiding tax payer do the paying (through heavy fines how else) - In fact I would like the criminal to pay so much that he also fully cover the cost of medical care, pain and suffering and the damages and stresses he caused. Arrive alive! and remember speed kills.