Print journalism has its own established method of drawing readers into stories with cunning, witty headlines, leading to longer in-depth articles and reports, but online the method is turned on its head.
Online, less time and energy is spent reading long passages or articles, thus headlines and opening paragraphs should bring to the front the facts; the who, what, when, where of the story.
The inverted pyramid is a writing style where the summary of the article is presented in the beginning of the article. This approach makes use of the “waterfall effect” well-known in journalism where writers try to give their readers an instant idea about the topic they’re reporting. The article begins with a conclusion, followed by key points and finally the minor details such as background information. Since web users want instant gratification, the inverted pyramid style, as supported by Nielsen, is important for web writing and for better user experience. From Smashing Magazine, Usability tips
Writing for the web
When creating, editing and designing content for the web, get the message across as quickly as possible.
To do that, say as little as possible, and put the most useful and relevant content first.
Speak plainly and openly and use a tone of voice that's appropriate to the audience. From Web design from scratch