Google+ should be Google, in the same way Gmail and Google Talk are just the same Google accounts. Someone said here today how he found Hangouts complicated on mobile, because it wasn't well integrated into the OS, the way Facetime is. And that's exactly why Google+ needs to become synonymous with a Google account. Apple allows you do use any and all of their services with your itunes account, from iCloud to payments, doesn't it?

You don't have to use it, just like people don't have to use all of Apple's services, and as long as they are not too in-your-face about it.