If something can 'break in', then it also follows that it will also, at some point, wear to the point that it is past it's optimum 'break in' stage. Engines wear out, they get broken in. Shoes wear out, they get broken in. Jeans do the same thing. Do the moving parts of speakers wear out, or does speaker failure have to do with damaging events (such as being shorted), rather than 'wear' over time?