There are a number of services designed specifically for tracking and connecting blogs. However it would be expensive for all the services to crawl all the blogs in the world all the time. By sending a small ping to each service you let them know you�ve updated so they can come check you out. They get the freshest data possible, you don�t get a thousand robots spidering your site all the time. Everybody wins.
If you bookmark the Ping-O-Matic ping results page you can simply load that directly and have fast pinging of almost a dozen services a single click away.