Writers are familiar with ambiguities within their fields of expertise, so creating such pages would be a natural extension of their abilities. Scope is another source of ambiguity. Users rarely know how much they are searching. Studies demonstrate that users intuitively believe that searches performed from the home page of a web site have much greater scope than searches performed from deeper inside the site. This behavior rarely happens.
Search technologies are still in their infancy.
With the growing quantities of information available today on the Web, there are no guaranteed solutions. Further, every project has its own requirements. A good analogy can be found in the descriptions for cookbook recipes. Invent results that handle any reasonable queries, even if the answers are outside the product's scope. For example, a software product that converts text to hypertext may not handle animated graphics.