Why "OK Google Now" instead of just "OK Google"? That seems like too much sub branding, which is something I usually associate with Microsoft (every Microsoft product is called Microsoft+SomethingElse).

They certainly want the prefix to all voice commands to be a low incidence sequence of phonemes for any language so that you don't get spurious activations and drain battery and/or accidentally execute a command, but I would think "OK Google" is a rare enough phrase that it would suffice.

A five syllable "wake up" command just seems excessive.