Except that appears to have finally changed with the 6 and 6+No.
As I understand it, the *DEVICE* takes the current it was designed to take.
In the case of an iPhone, this is 5W, regardless of the fact that there may be a 12W charger plugged in to the mains-the iPhone will only take the 5W it was designed to take and therefore won't charge any faster when connected to a 10 or 12W charger.