If the site: operator shows a URL from your site, then that URL is indexed.
But you can't expect the data from reports taken in different areas of Google to agree exactly - it won't. Asking which report is "real" is not a true question. There is no absolute "real" number - it's always churning. There is only what you see right now, and on this data center.
Tedster, I would have agreed with your answer before but I'm seeing some very strange things with site: . As most would agree, site: gives odd results at the best of times but now I'm seeing something new (which I was thinking about starting a thread about).
Lately, site: shows many pages which do not have a cached link. From my experience and observation, site: used to always show pages which were cached. Now it seems to in some cases show pages which Google is aware of but does not necessarily have in it's index for one reason or another.
Just noticed somethind odd. I tried site: on Webmasterworld (and I hope there is not a problem with me posting that link here, example.com just won't do) and I'm seeing hardly any pages with a cached link.
Why do most pages listed not have a cached link beside them? Yes, I do believe that WebmasterWorld is probably mostly cached but why are almost all pages not having a cached link? Am I missing something? I am seeing some sites with pages missing the cached links when using site: but doing this on WebmasterWorld, I'm having trouble seeing any pages with a cached link. Not sure what is up with that.
In summary, site: in my opinion is sometimes showing pages that are not cached by Google whereas one time it did.