Building backlinks to a web site is a key priority for webmasters who want their site to rank well in search engines. Because of this webmasters want to know that the links that they build to their sites are acknowledged and recognised by the search engines so they can get some rewards for the efforts they put in. Monitoring the link building over time is an important metric that webmasters can use to monitor their efforts. The search engines do not make it easy for webmasters to monitor this.
Google’s link: operator gives a small random sample of links to a website. Many newbie webmasters and link builders use the link: operator in Google to check their links and often jump to all sorts of false conclusions about what they see. They assume wrongly that Google only gives benefit to the links that are shown in response to the link: operator, which is not the case. What Google choose to show in the small random sample is simply that – its random. What is in the sample has nothing to do with what Google know about and use in the rankings of a site. Many years ago, the sample only used to consist of links that had a page rank of greater than 4, but it has not been the case for many years.
The reason Google only shows a sample is not known, but is probably to stop webmasters from getting too obsessed with checking competitors backlinks. In the Google webmasters Tools, they do show more of the links they know about.