Early newspapers were not the most organized. Facts, the most important part of a news story, were often burried deep in a story and difficult to find. The inverted pyramid changed that completely and made things much easier on the reader.
American journalists found that telegraphs could be unreliable. They developed a system of transmitting only the most important information in short paragraphs. These small transmisions often turned out to be the lead paragraph in their stories.
This turned into a good way to organize stories and it stuck. They would continue to support the lead with other paragraphs that contained facts of decreasing importance to the story the farther down it got. This is where the inverted pyramid name came from.
Besides making things easy of the reader, it also made the life of an editor a bit less stressful. Newspapers tended to print stories in order that they were recieved. The inverted pyramid made it easier for an editor to cut information that was less important in order to help fit the story in print.
The development of the inverted pyramid by american reporters was a neccesity. Anything that can be done to benefit the readers is a good thing. Today, it is the most common story structure in journalism, and it seems like it will continue to be for quite some time.