As AndroidRoot said, both. Think of the site as your brochure/shop. Think of the blog as one of your marketing tools. Once they are on your blog, subscribed to it through rss / email newsletter etc then you can point them to your site / product. But your blog has to be real genuine free good quality content for this to all work.
LOL I think a website business that has a blog is the best combination. Make sure the content of your blog is good like @willyc states though and you update it constantly with fresh ideas and content
websites is good for business and you can add blog in your website for news updating of your business .