Cross Network Utility and Networks

We see a lot of startups who want to build networks but they start by connecting with existing networks and providing utility that is cross network. Aggregation is a very common example of this. Cross posting is another.

I am certain that these cross network utilities can become good businesses but I wonder if they can become networks. We debate this a lot inside USV. I am in the doubter camp.

I'd like to explore this a bit today with all of you. If the initial utility of an app is to connect to a bunch of networks, collect information, present it, and then let the user engage with one or more of those networks, what incentive is there for the user to engage directly with other users of the app and help build a network inside of it?

Let's look at a few examples.

Take Flipboard. It is an excellent app. They innovated on the consumption interface in mobile and they present media and social media in an easy to consume and beautiful way. But is it a network and will it ever be?

Take FriendFeed. It was possiby the best UI for social media engagement ever created. But, because they allowed people to pull in content from and engage with other networks, it never really built up a network of its own. It could have taken on Facebook and Twitter. It was a much better Google+. But it sold to Facebook for what has now turned into a lot of money, but it did not build a sustainable network of its own.

Take Oodle. It pulls listings from lots of marketplaces, including Craigslist, eBay, Facebook, and showcases them in an excellent UI. But is it a marketplace itself? I don't think so.

There are a few examples I can think of where cross network utility has built a semblance of a network. Hacker News aggregates content across networks but by providing its own engagement platform, they have built a network. Reddit aggregates content across networks but because of the strong community elements in the platform, they have built a network. 

So clearly it can be done, but I am struggling to find a lot of examples where building on top of networks, instead of building your own, has resulted in a large network of highly engaged users. I'd love to hear more examples of that. Because this is an issue that keeps presenting itself to us and we are struggling with it.