The Google+ mobile web view on the iPhone and iPad has a feature that is not available in the desktop view. If you are in the stream view, there is a link under the Home button labeled Nearby. Tapping that link displays a stream of public posts on Google+ from people relatively nearby (within 20 miles or so from the looks of it).
You can return to your public stream view by tapping the Circles link in the Nearby view. Based on what I saw it appears that only a few people are posting to public streams in my area. I know there are a lot of active Google+ users within a 20 mile radius. It may be they are mostly posting to limited circles or not providing location information.