"When Does a Local Business Decide It Needs a Web Page?"
I would say the store first opens for business. If the store existed 10 to 15 years ago, it should have had a simple Web presence 10 to 15 years ago.
It's certainly a lot easier now to have a basic Web presence for little cost. As Ryan mentioned in the other thread, a Facebook fan page is free, and fan pages can be heavily customized.
Start a blog at Wordpress or Blogger for free. It would have a URL with something like "andyscarryout.wordpress.com".
Or buy a domain name like "andyscarryout.com" for one year at Network Solutions for $35. It's cheaper if reserving the domain name for more than one year or buying from another domain name provider.
Then pay Wordpress $10 per year to have the domain name point to the Wordpress blog. That way ".wordpress.com" won't be in the store's Web site URL. This makes the cost for a simple Web presence at $45 per year.
Wordpress provides many site themes for free, but it's likely that the blog/store owner would want more customization. Using custom CSS at Wordpress costs $15 per year. Now the total yearly price for a Web presence is $60 per year.
But it's unikely the store owner will know how to customize the blog design. The store owner may have to buy a custom theme or pay someone to do the design. Cost for this? Unknown.
Facebook, Blogger, Typepad, Wordpress, and some wiki hosted solutions and hosted CMS apps provide an easy or a fairly easy way for the site owner to add and edit content. That's the key. It should be simple for the store owner to modify the content on the site. The store owner should not have to go to someone else to change content on the site.
The store owner can post regular store hours, holiday hours, location, directions, phone number, e-mail address, store history, products sold, specials, new items, etc.
A simple Web presence may show up better in search results. Sometimes when I search for a local business, all I get in the search results are directory listings on other sites because the business does not have a Web site.
Play around by going to Wordpress.com and creating a blog for free.