You're missing the leverage that software gives you. A bakery that keeps track of its Yelp reputation and works hard to maintain a 5-star rating will attract customers from all over the city. It might even start attracting out-of-towners who are in for a visit. This bakery's "market" is effectively unlimited because in any major city, there are going to be out-of-towners flowing in and out on a regular basis, and some of them will be looking for a bakery.
A bakery that doesn't do as well at maintaining a good reputation on Yelp will have its market limited to reach of its advertising and the word-of-mouth of its customers. Now, in a relatively tech-heavy town like San Francisco, that might be fine. If you provide good croissants, you'll get mentions on blogs and Twitter, which would magnify the word of mouth effect in a manner similar to Yelp. But if your customers aren't bloggers or heavy users of social networks? You could have the best bread in the world and not be rewarded commensurately, simply because not enough people know that you have the best bread in the world.