What happened is that people continue to try an find new ways to get stronger. While some people can do quite well on a simple periodized program, like Coan, and Furnas, who was instrumental in Coan's progress, a couple of things should be noted:
1. Coan follows a simple, periodized program, but guess what? The numbers are based on percentages.
2. Do you really need a caculator for basic math?
3. Certain methods have been shown, both in practice (competition) and theory (research and study) to provide greater increases than others. Compensatory acceleration is one of them. The rational behind using the bands and chains is to not only make it harder to acclerate the bar as your leverage improves, working RFD, but to create additional muscular overload that is not only sport specific, but lift specific as well.
4. Using percentages as a part of training has been the hallmark of the most successful strength teams in the world. The most successful, the Russian Dynamo Club, has been using them for 50 years. This club was used as the basis for much of the Russian research that is the basis for the conjugate training system used by not only most of the members of this board, but Westside Barbell Club as well. Coincidentally, WSB is the best powerlifting team in the world.
People can go with what the masses do, but there is a reason they remain the masses, and not the individuals who push the envelope.
"Average athletes prepare with average methods" - Vladimir Zatsiorsky