The supposed top blog is http://boingboing.net/, which is just a clone of ebaumsworld.com and a hundred other joke/time waster sites like it. I do find it amusing that because the authors of these other sites don't sell conferences their sites are not considered "blogs".
The next most popular "blogs" are what I call product review sites. engadget.com, paidcontent and Techcrunch would be the biggest examples of this in the tech world. engadget.com/Techcrunch are fast growing product review sites that have a huge part of their distribution in RSS. Now what makes these sites so extremely popular? In my opinion they are popular for the same reason that news alerts are popular. NEW up to the date Information can be found extremely quickly and its very to the point. The only downside is these sites don't have a very good search so you can find old information. So in summary these sites aren't blogs, they are just product review sites with a far far better interface/distribution system.
Next you have corporate blogs, or people associated with a company. Scoble and Tara hunt, Om Malik etc all got big not because of what they had to say but of who was behind them. Each of these "bloggers" represents a corporation. I can draw comparisons to my blog here. No one who actually uses my site comes here to read this. This blog is read by SEO's, CEO's/Executives and the Media. I would sum it up as saying, in the old world you would release press releases and try and get publicity. Now if you have a blog and its widely read it doesn't matter what you say people automatically think its important. Blog popularity acts in the same way as google pagerank, the more readers you have the more publicity anything you say gets.
I think of blogs as nothing more then a distributed forum. Each blog represents a forum thread, and what sites like DIGG.com, Techmeme and bloglines etc are trying to do is recombine these separate threads into a forum again. The Digg.com model has no chance of winning, as less then 60 people out of 800,000 supposed daily users decide what everyone reads. The winner in this game will be the company that creates a personalized view of the "blogosphere". As i said before this would be accomplished by allowing users to filter out articles about games, graphics, movies etc etc etc.
So at the end of the day if you want to create a popular consumer facing website based on information/educating users you need to constantly display NEW up to the date Information and be very to the point with little to no advertising/distractions.