I see this complaint a lot when a G+ link is posted here, but Google never asks me to log in. Anyone know why it requires a login from some but not others?
I believe it happens when you are already signed in, but the session is expired (or is in some way not fully signed in). It then prompts you to finish the sign in so it can give you a good experience once you're there (for example, the ability to comment, +1, or reshare the post immediately, or add the author to circles).
If you have no session with Google at all, however, no login is requested.
