Why Does Google Treat "www" & "no-www" As Different?

Why Does Google Treat "www" & "no-www" As Different?: "site:www.domain.com - should show only www results. You want as many of these as you can to be fully indexed and not supplemental.

site:domain.com -inurl:www - should show only non-www results, but sometimes it also shows 'historical' www supplemental results too (see above for what I mean hy 'historical' - that's the May vs. September example).

site:domain.com - shows both www and non-www URLs and it can be difficult to untangle exactly what you are looking at.

site:www.domain.com -inurl:www - this is a 'feature', but it usually shows only pages with a problem!

That site:www.domain.com -inurl:www search logically says 'show me all pages from www.domain.com that do NOT have a www in the URL'. This returns ZERO results from the normal index, but does proceed to return some www URLs only from the Supplemental Index.

It is an interesting test. I used it last week on a big site to find the last 20 problem URLs. Ten were old URLs that just return 404 and Google is hanging on to them for the one year. The other ten were pages that had duplicate meta descriptions, which are now all fixed.

One more thing. When doing the site search, do it with 100 results per page to get a better view. Additionally, always try it both with and without &filter=0 on the end of the Google search url,enlighyning!