But there's more. Usability, and more generally human factors , is about continuously trying to improve your user's experience with your web site. Many people will only interact with your web site. They won't call you, they won't fax you, they won't talk to you. Your web site is your company so you need to make sure that it is easy to use.
Usability is a continuous process .
You must test real users with real scenarios. The data that you derive from this testing is gold. It is the information that you use to shape and mold your site for your customers. If you simply develop a site without this information, you are doomed to design a site that is focused on your ideas and your desires. While this feels good, this does will not ultimately boost your sales.