There is no question break-in occurs. Research has shown this to be true. However, what is at issue is whether or not the break-in is audible. From the break-in research "papers" that I have read, the electro-mecahnical differences, although they may appear vast, would never be discriminated in ABX testing.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated