It places the focus squarely on the news content and not on the users involved. There's no following and there's no cronyism this way.
In many services, such as twitter and quora, I've noticed that there is some degree of reciprocity that occurs even if it is neither expressed or implied that you should reciprocate. In fact, in most cases there is nothing written or unwritten culturally that says you should reciprocate, yet people do anyways.
By eliminating this you eliminate this falsely perceived social expectation of reciprocity, thus placing 100% of voting motivation on content. This is the right approach if you want stories and comments to make it to the front page based on quality of content alone.
You anyways don't know other users unlike facebook where most of the people liking and commenting on your status are your fiends.
More features they have, more complex it is for users and developers have to maintain it.