The way we understand information depends, in large measure, upon how we get that information. Most English punctuation marks are small, so as not to unduly interrupt the flow of letters on a printed page. However, on a computer screen, commas, periods, semicolons, colons, apostrophes, and many other common punctuation marks can be hard to see. More white space on a Web page makes it easier to discern individual visual elements, like words and punctuation.
Short paragraphs provide more white space, and also clearly differentiate points of discussion.
Short, simple sentences are faster to read and typically require less punctuation. Context can be a challenge. Because the Web offers little inherent orientation to its users, your Web writing must provide context in other ways. For instance, it's usually better to identify the antecedents of pronouns more directly and frequently in Web writing than in print writing. Conversational, and thus auditory.