Tumblr was not the first social media company to start its own network newspaper (for lack of a better term) but they are getting a lot of press from their decision to hire their own writers and editors and begin reporting on what's happening every day within their network.
The idea seems reasonable enough to me. Their network is comprised of millions of blogs and short of a crystal ball a new user has little idea what might be happening within that network on any given day. A journalism depart would certainly help them provide a resource for new users to discover what's happening, what changes are being made, what posts are most active, attracting the most attention or just providing really cool information.
Facebook, too, announced a similar move toward in-house reporting of site content, and Twitter has long been trying to find a way to organize and promote its wealth of content short of hastags and search.
The fact is these social networks have grown beyond the size of most major cities, even many states and countries. Facebook alone has more than 800 million users, all of whom are posting content, creating Fan Pages and doing 'stuff' every minute of every day. It makes sense they would need a journalism department to keep track of it all.
This is much like the way print newspapers were created. As humans gathered into more complex societies, formed towns and cities, people wanted to know more about what was going on; who was doing what, when, where and how. So, newspapers were created. (After we went the 'Town Cryer' route and created the printing press--but those are other stories.)
The idea behind what Tumblr and Facebook are doing is sound. Their networks are certainly big enough to warrant some sort of knowledge gathering service that can the parcel that information out to other users, just as some people today still rely on their local newspaper to know what days they need to put out their recycling, or when to expect the water rates to go up.
This move toward in-house news gathering is also a great way to help outsiders feel more welcome in these online communities; learn their way around and find the spots in which they will be most comfortable. I believe this will also create a new market for beat reporters interested in covering online communities and perhaps open the door to 21st century journalism.
Of course there is also the possibility that these efforts will lead only to self-aggrandizing and promotional pieces touting the benefits of these online communities while shying away from stories with any chance at being perceived as negative.
Only time will tell whether we are seeing the re-birth of journalism or simply a new form of advertorials.