With Google+ already being famous at a fast pace, with all the unique features and all that good stuff that cannot be seen or have been presented better apart from Facebook and Twitter, it would not be fair if it would be offered for those who only use Android phones and other devices. Knowing that there are also other social networking junkies using the iPhone, Google made it a point that iPhone users will also get Google+ for their app selection.
It also already available on the iPhone app store for free, and also offers the same kind of goodness presented in Android, such as the Instant Upload, the Huddle feature, and working in Circles. Even though it is not yet in full, due to iPad and iPod Touch limitations, people will still enjoy the new social networking platform on their powerful iPhones. There is no need to get through the learning curve, since it would be just as intuitive as Facebook or Twitter has been.
Source: Engadget