Blogs are whatever we make them. Defining 'blog' is a fool's errand.
I think it is equally tiresome and useless to argue about whether blogs are journalism, for journalism is not limited by the tool or medium or person used in the act
I'm not sure blogs are necessarily the best place to get a pulse on anything. People want to blog for a variety of reasons, and that may or may not be representative.
Blogs are for anoraks who couldn't get published any other way.
Blogs are a great way to monitor and even participate in the chatter about your new site.
Blogs tend to consist of much shorter entries, many per day, the blogger seemingly striving for communication more than self-enlightenment.
We of the genus Homo ride the logs that float down the Round river, and by a little judicious "burling" we have learned to guide their direction and speed. This feat entitles us to the specific appellation sapiens. The technique of burling is called economics, the remembering of old routes is called in history, the selection of new ones is called statesmanship, the conversation about oncoming rifles and rapids is called politics. Some of the crew aspire to burl not only their own blogs, but the whole flotilla as well. This collective bargaining with nature is called national planning.