Because people think users don't scroll. Jakob Nielsen wrote about the growing acceptance and understanding of scrolling in 1997, yet 10 years later we are still hearing that users don't scroll.

Research debunking this myth is starting to pop up, and a great example of this is the report available on ClickTale.com3. In it, the researchers used their proprietary tracking software to measure the activity of 120,000 pages. Their research gives data on the vertical height of the page and the point to which a user scrolls. In the study, they found that 76% of users scrolled and that a good portion of them scrolled all the way to the bottom, despite the height of the screen. Even the longest of Web pages were scrolled to the bottom. One thing the study does not capture is how much time is spent at the bottom of the page, so the argument can be made that users might just scan it and not pay much attention to any content placed there.

Here is perhaps the biggest problem of all. The design method of cutting-off images or text only works if you know where the fold is. There is a lot of information out there about how dispersed the location of fold line actually is. Again, a very clear picture of this problem is shown on ClickTale. In the same study of page scrolling, fold locations of viewed screens were captured, based on screen resolution and browser used. It's a sad, sad thing, but the single highest concentration of fold location (at around 600 pixels) for users accounted for less than 10% of the distribution. This pixel-height corresponds with a screen resolution of 1024X768. Browser applications take away varying amounts of vertical real estate for their interfaces (toolbars, address fields, etc). Each browser has a slightly different size, so not all visitors running a resolution of 1024×768 will have a fold that appears in the same spot. In the ClickTale study, the three highest fold locations were 570, 590 and 600 pixels -- apparently from different browsers running on 1024X768 screens. But the overall distribution of fold locations for the entire study was so varied that even these three sizes together only account for less than 26% of visits. What does all this mean? If you pick one pixel location on which to base the location of the fold when designing your screens, the best-case scenario is that you'll get the fold line exactly right for only 10% of your visitors.