Another reason for the coiled cable, is that you get a warning before you hit the limit. With a straight cable something has to give suddenly.
This isn't necessarily true as tension is created at the headphone jack as soon as the coil begins to stretch. The cable can pull out before any physical limit. This can't happen with a straight cable. Also, coiled cables when they are not stretched are obviously not equally distributed in weight so when they are dangling are causing wear on the headphone jack. This can cause problems over time.
Have you ever listened to a headphone with the coil constantly stretched? It is an awful experience.
