The site command (site:www.domain.com) is often used to determine the health of a web site in a search engine. The thing is, Google's site command is far from accurate and too many SEOs look at it too closely. We discussed this before and I just want to cover it again.
Googler, JohnMu, said in a Google Webmaster Help thread:
Focusing on the site:-query rough approximations will not lead to useful results.
Did he just say that the site command results are not useful? Are you surprised? I'm not. Like I said, we said this before.
For example, a site:www.seroundtable.com command returns for me over 17,000 pages. When I look at Google Webmaster Tools, I see indexed URLs at 9,921. So who do I believe?
We discussed the site command dozens of times here over the course of about 6 years. It is interesting to see how this has changed over the years.
Forum discussion at Google Webmaster Help.