While most people would argue that blogs and websites are open, few would argue that *Google* is open. So this is a curious place to begin thinking, and yet structually, it is actually quite apt.
PDS'es are like blogs, the rest is like Google. But relays/appviews/etc do a lot *more* than Google.
Relays, AppViews, etc don't just index information. Blogs and their interactions are generally slow-moving, but social media is direct and responsive. Notifications and fast interactions are key. So search engines, yes, but we should also think of these components of doing much more.