You see it in all the news coverage. People refer to Siri as a person. It gets into your brain. Have you seen normal people showing off Siri to their friends? They are giddy with excitement over having a personal robot voice in their pocket that knows them by name.
I feel google doesn't employ anybody who has an average family or knows average people. Normal people don't know how things work. What's a "Google Now?" You'd have to look up a definition. It's about ten different things jumbled together under an Enterprise-Grade Naming Convention product umbrella.
Look at the Google Now product intro -- "Google Now has prepared an alternate route for your commute." People have to learn "Google Now" is a product and/or service that does specific things. People simply understand what Siri is after seeing someone else use it for a few seconds.
Even the Google Now tagline requires a level of mental disambiguation: "...with the predictive power of Now..."