Almost all other websites on the Internet are based on a vertical form, in which you end up using your vertical scroll bar at the right hand side of the browser if the page is larger than the size of your browser window. There are even some inventions centered around this quasi-standard way of doing things. If you think about it, this scroll bar rarely is used on everyday web browsing. This effect is simply created by using a really wide table that has other tables inside of it to keep the information in line.
Nobody ever tries such crazy things anymore.
In the end some people actually rather like the panaromic effect that you get with a side scrolling website. It all comes down to what works for you. For example if I wanted to make a graphical timeline of events, it looks more natural to orient the timeline horizontally. Thus a side scrolling site becomes useful. Horizontal orientation gives one a sense of chonology.