It just gives your ears a chance to become accustomed to the new sound of the speakers in question. Once you get used to them, you are able to get past how different they sound compared to your old speakers and start listening to them with out bias.
As I mentioned in earlier posts on the subject and Alan more or less agreed, break-in suggests as the speaker wears it sounds better.
If a speaker shows enough audible wear, in that short time frame manufacturers suggest, they should be sounding terrible after a few years of use due to even more wear and tear.
