I'm not sure why you mix Android, iOS, Facebook and G+. Sure, Android systems tap into existing Google products for some features, but this is not exclusive. The Facebook app, as far as I can tell, works nearly the same on Android and iOS and can also tie into the other infrastructure like contacts. In my experience nothing on Android makes you more likely to use G+.
Especially because G+ is more technical in its uses it caters to another target group than Facebook which I find really refreshing. I don't use G+ for my "real" social life at all, but mostly for my social activities related to technology. Getting those two things separated was a huge step forward for me. Now I don't bother my real-life friends with technology related posts anymore and can take them to an audience that is more likely to be interested.
Especially because G+ is more technical in its uses it caters to another target group than Facebook which I find really refreshing. I don't use G+ for my "real" social life at all, but mostly for my social activities related to technology. Getting those two things separated was a huge step forward for me. Now I don't bother my real-life friends with technology related posts anymore and can take them to an audience that is more likely to be interested.