The iPhone integration on BMW's is good but not great. I just took my car in for service and they gave me a 2012 C300 4Matic. That thing has the sickest integration with the iPhone, and the best part is that you can play music via Bluetooth. As far as I know, you need the iPhone plugged in to the BMW adapter to play music.
On the Merc, you can play music with your phone in your pocket. Many less expensive vehicles/brands also have this feature. You can do this with Ford SYNC, Buick Intellilink (great name... ha), and others.
Despite how cool I think it is, here is an article giving 5 reasons why it isn't:
Most notably being lower audio quality... which I don't notice.