On the Web, it doesn't matter how many pages you use or how many colours, but whatever you produce has to travel along a cable from the server to the reader's computer - and that takes time. The more information you send, the longer it takes. If you try to put too much information on one page, it takes an unreasonable time to render on the reader's computer screen, they get impatient and go off somewhere else. So, with a Web page, you have to get your priorities right from the outset. Information comes first and decoration or bells and whistles should either be ignored or very much played down.
Information has to be delivered in digestible chunks.
You will appreciate how in print, the resolution of an image is related to the quality of the paper. Type is rendered at something like 2400 dots per inch on an imagesetter. On any computer screen, there is only one resolution for images and type alike - 72 pixels per inch. The size of the pixels may vary slightly from one monitor to another and even the size of the inches, but the 72 PPI resolution of a Web page represents the borderline between having visible individual pixels on the screen and their blending into one another to form a smooth image. This too comes down to simple economics and cost effectiveness.