Should you need a third party app installed for a good reading experience? I don't use Google+ and don't want the app on iOS, even if it was launched when I click a Google+ link (which, fwiw, you are correct: it currently does not).
(On the other hand, Tumblr looks great on mobile, and it doesn't need an app. Facebook, too, is at least readable on their mobile site.)
I never understood why websites created apps of their websites. The browser is ubiquitous. Use it. I don't want to install seven different apps for my seven favourite sites. I don't see why this is acceptable on a mobile platform any more than it would be on a desktop platform.