At last count, there were over 2,400 magazines and other like-publications available for the public to pick up and read. Or, more to the point of this series of blogs, for companies to advertise in. That's definitely a lot of choices to make.
The reason for this large number is that specialization has become the name of the game in modern publishing. Look at your local book store, and head to the magazine area. I guarantee that inside you'll find a publication to fit your specific interest, hobby or industry!