Why do cables need break-in?

I just had the experience of having newly introduced speaker cables (AudioQuest AQ-8 bi-wire) break in. When I put them in a few days ago they sounded thin, bright and lacking in bass. Now, after 4 days and 40 - 50 hours, they sound far better: relatively neutral frequency spectrum with much more bass weight. I'm delighted, of course, but I'd like to know why this happens. Will I experience the same scenario when I change interconnects?