Annalee Newitz nails it:

You could argue that Tumblr is basically really, really simple syndication. You find the Tumblrs you like, you subscribe to them, and poof they show up in your Tumblr profile view. Or you follow people on Facebook to get the same thing. But both Tumblr and Facebook are silos of information. RSS feeds can be generated by any publisher, from the New York Times and Blastr, to the Nature journal and your favorite obscure porn repository. Tumblr feeds come from, well, Tumblr.

In this way, reading Tumblr is a lot like reading a paper magazine. Every story in the paper version of Wired comes from Wired. It's the ultimate information silo.

...

Magazines like Wired and the New Yorker have been able to transition more smoothly to the digital world than newspapers did a decade ago. They are porting their magazines directly into apps that silo content just the way paper magazines do. And many new online publications like Matter and The Atavist are following this model, creating apps that hold their content rather than syndicating them via RSS. Older publications like Huffington Post and The Atlantic are going the other direction: they are looking more and more like social networks.

Meanwhile the archetypical blog, which gained readers by sending out its RSS feed, is slowly becoming a digital anachronism. Of course a blog can be much more than a publication that uses RSS, but it's worth noting that the popularity of the word "blog" has declined in recent years just as RSS has. Nowadays it's more common to hear a blog referred to as a "website," or "online magazine" or just "a publication."

So where does that leave us, as we look to the future of media technology?

We are returning to a world where what you read online comes to you in silos. Instead of a feed reader, you can get an app that organizes your app subscriptions on a nice digital bookshelf where they look just like a bunch of paper magazines in a bookstore. But unlike an RSS reader, this app doesn't ever mix the content of these magazines up into a single stream. It keeps them separate. You have to jump out of one app and into another to read the next magazine on your shelf.

We are also moving toward a reading style that requires you to visit a specific site in order to read, instead of pulling all the articles you want into one piece of software. You go out into Tumblr and Facebook. You don't aggregate all your favorite Tumblrs and magazine articles into, one, unified reader. Everything is separate and out there, in the cloud.

This is how we used to read, back in the 1950s. You went out to a bookstore or magazine shop, bought discrete bunches of bound paper, stacked them on your table at home, and read them one at a time. Sure, you could browse a bit in one magazine and then move on to a comic or book. But you always knew you were leaving one and moving to the other.

The pendulum is swinging back. The only place these days where everything truly mixes together is... WAIT FOR IT... Twitter.

Oh. Em. Gee.

What have we become?