Given that about half the traffic on SO is asking about Objective-C related issues, how could asking to find the "mother" reference possibly be "only relevant to a small geographic area", et al??
From the "Too Localized" message:
Any answer would only apply for right now. It might not apply for next week. Or next year. Or five years from now, when linked references die.
The reason this does not apply to general technology questions is that the questions tend to presume or outright indicate a specific version. If I ask a question about jQuery 1.4, correct answers to that question will always be correct for jQuery 1.4 - no matter what version is the current one out.
For the record, "Not Constructive" and "Off-Topic" would also be appropriate reasons to close that question.
I generally choose "Too Localized" as a proxy for General Reference, when the answer to the question is "Look in the manual, or do a Google Search." I admit that this choice is not without controversy.
Too Localized is especially apt for the question you linked, since a Google Search only turns up older versions of the book you requested. Consequently, it fits into Joel's archetypal example of:
As you can see, choosing a close reason for questions that are the "perfect storm" (i.e. they meet several possible criteria for closing) can be difficult, as people will often argue about the veracity of the close reason instead of the more pressing issue, which is that the question really doesn't belong on the site anyway.