Why? Because it's the only book on web design you need. When a visitor reaches your site, he's presented with options. Learn more about your company, read testimonials, coverage area, etc. He's bombarded. And that's not good.
Obviously you want to present information that's relevant. This info should be presented "above the fold" to use a newspaper analogy. While it might be tempting to fill your site with a long history of you and your business, most people don't care.
What they do care about is how to get in touch with you. If you own a carpet cleaning business, I don't need to see 100 pictures of you standing in front of a company van, and I don't care that your business was started in 1994 and has grown. I care about getting my carpets cleaned and that means getting in touch with the company.
If your existing website doesn't feature a phone number or contact form prominently displayed, you might want to find a different web designer. I know, I know - this site doesn't feature those things, and that's on purpose. But the vast majority of the sites we see and work on do.
Your conversion rates will sky rocket because LESS IS MORE. Don't make a visitor think when he hits your site. You only have a few seconds to get to the point before he clicks "back" and is on to the next (competing) company's website.
Also - make sure your contact form works. This happens way too often and there's no excuse for a non-functioning contact form on a website. It makes you look amateurish and only frustrates the end user.
Your website doesn't need to be flashy. In fact, the opposite usually works better. People don't want Youtube videos exploding on them when they hit your site. They don't want 100 links to sift through. They want a clear, concise presentation about who you are and what you can offer them.
If someone really wants to read about the history of your business, or view a slideshow, they will seek it out. And that's fine. But most people are as busy as you are and just want to speak with someone about their problem/need. Make it easy and you'll get more business.