Recently a customer asked me what difference it would make if the CEO of a company were the author of a blog but didn't allow comments? My immediate answer was that that I didn't think that they should have a blog if they had no intention of allowing comments. For me a blog is something that allows comments, even if those comments are criticisms. How you address criticism can be particularly powerful.
I feel that if don't wish there to be comments, then frame the site that way - more like a news service. For me at least, blogs are an opportunity for two-way communication. It's a venue to interact with customers and advocates of your company. Feedback allows for an opportunity to improve.
Two-way blogs are fantastic brand tools. It empowers your audience and gives you front-line exposure. Shutting down conversation harms your brand by making your reader suspicious as to why you refuse to listen. Why is it all about your opinion when in reality it's all about your customer - or it should be.
Think twice before you shut the door on your customers.