It's true that a new speaker system will sound different over time, but it has much more to do with the listener's perception of the sound changing over time than it does with the speaker actually undergoing physical changes over time. It makes sense when you think about it. A new speaker in your own home will have a sound that you are not used to. As you become accustomed to the sound, the way you perceive it changes.
This is similar to something I call the "barking dog phenomenon." Many of the homes on my block have dogs, most of which will bark from time to time when they are outside in their yards. I barely notice it when they bark since I'm so used to hearing it. Occasionally, a new or visiting dog will bark and I really notice because it's not something I hear regularly. It's not any louder than the other barks, it just doesn't sound the same as the barks I'm used to hearing. My brain is more acutely aware of that new bark since it hasn't been filed into the "normal" category. If that dog stays in the neighborhood, over time its bark will be filtered into the background noise along with the others.
