noise cancellation
if these are legit, this is pretty great - almost for sure those slits on the buds are mics for noise cancellation, meaning that the processing is being done at the phone level, and opens the door for headphone manufacturers to build really nice buds with this built in for fairly cheap (current noise cancellation headphones have do their own processing).
it also means that almost everybody that gets this is going to get a big bump up in terms of sound quality from the old style - it won't be audiophile quality, but most people that invest in good headphones know how it can make a dramatic difference in your music experience, and this will almost certainly be one of the new iphone's major selling points.
being able to eliminate outside noise allows you to really hear your music. an interesting experiment is just to take your current headphones, and listen with just one bud in while you are in a noisy environment, then put the second one in, and compare what you can hear. it's not a scientific experiment, but it goes a long way to showing you how your perception of the music changes when you are hearing other sounds.