Ironically, Apple's services like Maps and Siri are the ones that are not very "integrated" but are quite "fragmented" instead, since they need hooks into different databases from 3rd party vendors of which they have no control on, while Google only uses their own Google search engine for Google Now, and their own Maps database for Maps.

Also, Google has already brought Voice Search to the iPhone. I think Google Now is also a service they'd like to bring, since it seems like one of those services where they would benefit if it was on the most popular mobile platforms at least.