That's a pretty big claim. I think most would agree that a 'most powerful' blog would be thought provoking, world influencing, maybe even mountain moving. These blogs are... kind of.
I think the vast majority of these blogs can be categorized into one of seven areas: celebrity gossip (Perezhilton anyone?), sexuality, special interest (like cooking, philosophy, even World of Warcraft), business, news, opinion, and diary/anecdotal.
Some of these blogs have changed the world around us. They have influenced - like the article says - presidential elections and senatorial impeachments.
That being said, I don't think celebrity gossip will never bring change the world should believe in.
Nevertheless, these blogs have flexed their muscles and proven their influence. They are read. People's worldviews are shaped through the content they devour, thus affecting how they interact with the rest of the world.
An avid twinky eater is not likely to run a marathon. Their diet influences them.
Similarly, people subsisting on junk media for information are predisposing themselves to engage the world in a particular way. They will talk with co-workers about particular things. They will show their peers and children what they believe to be valuable, no matter how heart-healthy those snacks may be.
These blogs also show their power by influencing the blogosphere. They are adding elements of personality to the digital world that provide an electronic edge in the marketplace, er... MarketSpace, of ideas. These elements enable readers to choose a blog they connect with, and potentially leave others behind. The strongest blogs survive.
This process helps tailor the contents of the blogosphere to meet the desires of different facets of society. It produces genres as bloggers struggle to find a niche or merely advance their personal opinions and experiences that others agree with or appreciate.
Are all these blogs helpful? I don't think so.
Are these blogs powerful? Yes.
Check the article out for yourself and share what you think.