New speakers are like a new pair of jeans - the material in the surrounds and spiders are stiff and need to loosen up with wear. No magic, just materials science. Paper surrounds requires more break-in than butyl rubber, foam is in between. Down the road, foam typically disintegrates first, then paper, and finally butyl rubber. A lot also depends on the environment. Light, especially UV is death to foam. Humidity, too high or too low causes problems with paper. Heat causes its own set of problems, especially with electrolytic crossover caps. So when you consider all the variables, there are lots of reasons why speakers vary in break-in and also break-down.
