Too many comments on the original article for the time I have this morning.  Still, one thing popped out at me from Danny's article (concerning estimated hits changing when you modify a query):

...Adding that extra word should give you a subset of the original query. It should come back with less results, not more….

I would not expect or want a search engine to limit itself to a subset of a query just because I add a word on to the end.  An exact match query (where you embed the terms in quotes) should behave that way but a broad match query should in many cases INCREASE the number of relevant hits as you add more words, unless you're just focusing on rare words.

A search engine has to infer intent from the query and very often people use a sort of reverse or abbreviated logic in forming their queries.

Hence, the search engine has to be careful about when or where they filter potential source documents from a query.  If the newly added term is vague and ambiguous, I would expect the query to change its mix.  However, if you append a well-established location name to the query, or maybe a date, then perhaps the search engine can infer enough intent to filter potential sources better.