I will try to mention some of the course changes that pertain to the preparation of a diver to act as a member of a buddy team, so as to dive unsupervised. This does not include resort or other courses that quickly allow a person to be taken by the hand in warm clear vacation locations:
1. Reduced the level of in-water competence required.
Generally this decreased the swimming distance and some organizations allow the student to accomplish the assessment by using fins.
Comment: The amount of swimming ability required, is directly proportional to the environment where you dive. It is my experience that a lower degree of in-water ability of a diver is directly proportional to the panic time ratio. It seems reasonable that a person who is strong in the water is mentally and physically better prepared (all other things being equal) than a poor or non-swimmer in the water.
With all due respect, in my sons and wifes training there were several 17-18 year olds that were on the swim team and swam VERY well. But two of these kids dropped out due to not being comfortable "underwater". The instructor tried to talk them into staying in the class, but they would not have it. This was in the second and third week of training that they dropped out.
2. Confidence and familiarity
Many courses today do not allow the time necessary to build confidence in the use of equipment. Again, this is less noticeable if the students open-water experience is in a warm-water vacation environment that resembles a fish-bowl.
Skills like doff and donn, bailout and black-out drills (under mild harassment) can build confidence in both the equipment and the students ability to deal with a unexpected situation. These types of skills have been also used in the training of military and commercial divers and they have been proven to increase confidence and save lives when the diver is faced with a problem. I'm aware that we're not training military and commercial divers here, but the same techniques can in-fact better prepare a sport diver in case of an emergency.
3. Rescue skills
Rescue skills were included in the basic program. Some courses today may or may not include this. If a diver is to be an effective member of a buddy team, s/he must be able to understand what to do if a rescue is required.
4. Dive planning and air consumption
Divers had to be able to plan their dives and project there air consumption accordingly. Tide tables were also included. Basically if a diver is expected to dive unsupervised, they have to have the necessary skill-sets to select a safe diving area. Less emphases is on these skills today.
5. Buddy breathing
This was a mainstay that I still agree with. No doubt that this will open-up the debate even further.
These are a few areas. Obviously this is not limited to one organization, as most have lowered their minimum standards. Even 40 years ago, the level of training required was evident in the number of hours of training each organization required.