Perhaps you are thinking of notifications, they behave as you describe. I am talking about my stream, or someone elses stream of posts, or a post as a unit. The comments ride along with all of them, in their entirety. They may be in some state of partial collapse, but they are always there.

Looking at my stream, by screen space the comments generally occupy about 1/3 as much real estate as the parent post. On posts I've never interacted with.

This is by design obviously -- and when the comments are good, its great. When the comments are bad, its bad. Time will tell whether G+ ends up with the type of community that can support this very in your face community intensive model.