The integration between iOS and Android Wear is necessarily different than the integration between Android and Android Wear. Presumably, it taps in to notifications in a similar way as the Pebble, so iMessages, for example, probably aren’t very workable on Android Wear. The devices it works with are still extremely large and incredibly gross, too.
I have doubts that this will affect Apple Watch sales. There are other third-party smartwatches that work with iOS, like the aforementioned Pebble, and they have similar capabilities, though without Google Now support. My hunch is that iPhone users who buy Pebble and Android Wear smartwatches will do so because they’re kind of interested in smartwatch-y things; Apple Watch buyers are probably more interested in the seamless ecosystem.