[kevincox]

Most high end phones now days have the option to have an always listening microphone for almost no power usage (1 or 2 percent over the day on my Galaxy S5). So if you leave your phone in the middle of the room it works quite well, and often you can even shout at your pocket.

But I think you are right, it's the small improvement over the phone, you always know where it is, and the microphones are designed for large area reception over phone microphones which are generally optimizes for closer sound sources. These small differences are valuable, even though you can get 90% of the functionality by just keeping your phone in the open.