It doesn't really make a difference. You can save a URL with or without the WWW part and type that into your address bar and still go to the same site. You can set up a redirect so that www always or never shows. Sometimes people skip the WWW part because it looks better as well. Aparantly though, you should always save links the same else spiders can think it's 2 different sites and not give you credit for one.
Its the CNAME record for host "www" is not added in the Total DNS control panel. Either way, its the same. or the webmaster can set up redirect from non-www version to www version.
I've wondered this as well. However, if they really are the same, why does a search say "not found" if you put in the www?
www is just a subdomain which should be added by you or the hosting provider.When you purchased a second level domain,you have the right to determine its subdomains.
Sometimes if you make changes to the site. It can make the search engine confused until it catches it again and adds the www. to the site IMHO. I have seen it before.