There are 2.2 billion internet users in the world, (find this statistic and more at Internet World Statistics) spending £591 billion online in 2010 (find these statistics at IMRG). To reach an equivalent audience by other marketing means would be staggeringly expensive compared to the set-up and running costs of web site.
Almost every visitor to a web site is what a sales person would call a 'hot lead'. They want what you are selling!! So as long as you have a well designed web site that sells your company and makes it easy for the customer to purchase, the business is sure to follow and you will get a good return on the cost of the web site.
Back to benefits of a web site