This was one of the first things I noticed when I got my 6S. But not in a bad way. Apple hadn't mentioned just how fast Siri would be. Just like that article states, there is absolutely no reason to give feedback that Siri is listening when it is instantaneous. For those that say they just like to know she is listening, any feedback, whether haptic or otherwise only serves to slow down the process. One would naturally wait until they feel it, or otherwise think that they made a mistake and started speaking too soon.