Peter,
I'm of the opinion that if more folks took the time to cast different rods of the same relative length and line size, they would see how different rods compare to each other. They would also have the benefit of feeling slow, medium, and fast rods and thus know with certainty what is meant by fast, medium, and slow action instead of parroting manufacturer add copy. Doing so would also allow a person to see that if he likes a certain action in a single-hand rod, he will very likely like the same action action in a 2-hander and thus avoid buying rods ill suited to his preferences and casting style.
This would certainly go a long way to make action nomemclature more standardized and understandable. That way when a person says fast-action or slow action, or tip action, or progressive action many more people will know what is meant.
The first time I did the side by side casting with the same line and length rod it was with a GLX 15' 10/11 and a T&T 1511. The experience was invaluable. Immediately after casting these two rods, I cast a T&T 1409 and a Redington DFR 14' 9/10 along with a St. Croix 14' 9/10. As you said, it was a very educational experience.