In a pre-literate society, when most people were unable to read or write, the Town Crier was responsible for making sure that everyone knew of the important events. The development of reading and writing, and especially the invention of the printing press, put the town crier out of business. It was easier and more efficient to print posters or newspapers. In the 1880s through 1930's, the equivalent of the "town crier" was the newspaperboy who shouted out the headlines as "Extra!", meaning an extra lat-breaking edition of the paper.
We still have a Town Crier; his name is Matt Drudge, and he is the modern equivalent of the paperboy shouting headlines to sell papers. Every blogger in the world is doing the same job; pointing out important information that you may have overlooked.