Why does Google sometimes display more pages than can be viewed?

Question

Take a look at this query: http://www.google.ca/search?q=site:stacklist.quickmediasolutions.com

At the bottom of the page, it shows 5 pages, but when I click on 5, it jumps to page 3.

Why is that?

Answer 1

This can sometimes happen when there are similar pages that were indexed:

In order to show you the most relevant results, we have omitted some entries very similar to the 19 already displayed. If you like, you can repeat the search with the omitted results included.

If you click the link at the bottom of the last page, you should see all 5 pages.

For more information, you can see this book which explains about that feature.

It seems like this is also for optimization reasons. From Google's page:

In addition, when you click on the next page of search results, the total number of search results can change. In this case, we realize that some of the query results are duplicates, and collapse those duplicates so that you can find the specific result you're looking for more easily. Collapsing the duplicates decreases the estimated number of results, as well as the overall number of results pages.

(emphasis added)