Enrico Altavilla reported on Google+, Never use the number of search results reported by Google for Serious Decisions because the results are misleading.
He also said,”Site: your website name” is OK for small sites to check the pages because they have small numbers of pages but for large numbers of pages(We are talking here about the dynamic sites, which are having lot of dynamic pages generated over the time.)
He also attached a screenshot of the report he used to check for the thousand of pages to check about this experiment by using 410. But the results are completely not genuine. Where as the results in-terms of indexing is quit real from Sitemaps or by using Index status in Webmaster.