I agree that voice commands are sometimes useful, but they also sometimes aren't. One problem is that voice is more reliable when it has context, like a complete sentence. That doesn't always fit the use case of openign an oddly named app.

Another problem is typified by a commmon Android Wear app which allows you to request a fake phone call on your phone. This example shows one of the use cases for a wearable: its a device you can look at when its socially or physically awkward to pull out a phone. You don't want to say, "Google, this meeting is boring!" But you might want a button that lets you do something about it.