Using a blog for business purposes is a tricky proposition. The main reason for doing a business blog is to increase sales or readership, but content that is purposed at selling a product or service is generally ignored by the public. A blog works best when there is a loyal readership and community interaction, but you will not get that environment if your blog talks about the new product you have put out or your sales figures for the quarter. And while the cost of blog is effectively nil, with the exception of the time spent writing it, it can still be hard to justify the expense of something that is lined up to fail.
The usual workaround for this is to have a blog that focuses on your industry rather than your company, but it is a rare company that will accept that plan. Without a call to action for the companies products, there is nothing stopping the reader from using the blog for information only and then going to a competitor. A blog with a sales message will just cause the reader to close the page with no further actions. It is a rare combination of talent and company approval for a business blog to be a justifiable endeavor.