The online edition of Courier & Press quotes a law student blogger who says that there are basically two types of blogs: blogs that comment on the current scene and blogs that are maintained as a personal journal. Although grossly simplistic, if you had to put blogs into two categories, I guess that might fit.
Personally, I think blogs could go into several important categories, one of which would be information rich blogs. That is, blogs that collect information in certain topic areas and then add comment. There are a large number of blawgs (law blogs) that would qualify in this area. Among the blawgs, many are specialized into legal areas, like copyright law and so on. Many others comment on general law topics.
So, to say there are journal blogs and comment blogs would be like saying there is vanilla ice cream and chocolate ice cream. Yes, that's true, but there are a lot more flavors if you look.