Ambiguity, Ostention and Description

Pat Hayes' In Defence of Ambiguity, presented at IRW 2006, has been on my desktop for weeks, and I take it as the most challenging food for thought currently available about the Semantic Web. If you have not yet read it, you should now.
There is only one point on which I would argue. Pat holds that reference can be made by ostention (gesticulation showing what you are about) or description. All Pat writes thereafter about description being inherently ambiguous, I strongly agree with : disambiguation being a contextual process, the more precise the description, the more ambiguity you get, and so on.
But I would hold that ostention is as ambiguous as description, so that reference is ambiguous in nature whatever the way it's done.
Suppose I am holding a book and ask you : "Have you read this?". The reference to "this" is by ostention, since I seem to hold and show "this". But the "ostentatum" indicated by "this" is actually some copy of some edition of some book. Does "this" refer to this specific copy, which happens to be my own personal copy (maybe annotated in some way), or is the referent the particular edition of which this specific copy is a sample, or is it the abstract entity, the book independent of any physical support, of which what I am currently holding happens to be some physical avatar? Every one of those interpretations is meaningful, and only the context of the conversation might disambiguate. So even with ostention, there is ambiguity left.