The reason people go for the information sites is that it's often harder to get ranked for products than it is information. Let's say you're trying to compete for the phrase diamond jewelry. Well you will be competing with all the popular diamond retailers.
Remember, the way to get on page 1 of Google is to have a ton of people recommending you and linking to you using the keyword phrases you are targeting. The average person looking for diamond jewelry would go to their favorite retail stores and even if they did search for diamond jewelry they are going to find the major stores.
It would be difficult for you to compete with them because what is going to encourage other people to link to your site when they can go to reputable sites to buy diamonds.
Now unless you have some incredibly low prices for the product / keywords you are targeting then it will be hard to compete. Remember you have to get a bunch of people to link to you in order to boost that Google rank... especially if it's for a popular phrase.
But if you create a content rich site about diamond jewelry for people who want information about diamonds (type of cuts, etc.) and you build your site up with tons of great info. People may begin linking to you because you are becoming a great resource for diamond info. In the long run this may help you compete with some of the top retailers for various diamond searches.
Take Ken's daughter's site, anguilla-beaches.com. If she had just tried to optimize for "anguilla tickets" or "tickets to anguilla" she would have been competing with Travelocity and all the popular travel sites. But because she decided to start with basic information about the island of anguilla, she created a site like no other out there and people began recommending her.
If you want to start out by selling products and optimizing for the product name, you better make sure it's in a niche that's not very competitive and very specialized, otherwise you'll have a hard time beating some of the major retailers.
So even though the information route is more work, it gives you a chance to become an "authority site" on the topic/keywords of interest. Authority sites with tons of backlinks is what google is looking for and if you can't get people to link to you, your traffic will be limited.
I hope that makes sense. I know I was rambling.
