Why would a business would put their business in the hands of another company ?
I had a business owner tell me they didn't need a web site because they had a Facebook Page. In the weeks that followed, Facebook changed many of their policies and the company's Facebook Page looked nothing like it had before. The company had no control over the change to the content layout and the algorithms that determine how many Facebook users see their business page.
Should you not use Facebook ? No, you should use every marketing and social avenue you can. Your social networking presence should lead visitors back to your web site for more information to build your brand and client loyalty.