While the web and the sites on the web are certainly accessable to all kinds of people - not all sites are designed for or targeted toward all viewers. I imagine that the owner of the site you cite is only thinking of his site in terms accomplishing one task eventhough the site could be used to accomplish more than one task.
This is not necessarily a design or "standards" issue but a management or business decision. Is it the best decision for this company? Maybe they are "missing the boat" or maybe it makes good business sense for their needs - it fits their business/marketing practices.
Should there be such a standard/guideline? If there is a standard, who would enforce it and what real impact would there be?
A successful website follows some standards or practices ( for navigation, coding, and content) and is designed to communicate its` message to a target market... hopefully, in an effective manner. But it is up to the site owner to decide that target audience.