When is a link considered a link by Google? If I do a search for the name of my domain I get a few hundred sites listed, and most of these sites are linking to me, but if I do a link:[URL] search, I get a much smaller count.
Why are some links considered links and others not?
A site is only listed when searching for backlinks if you are receiving a set value from that page. If the page has a PR of 1 and there are 50 links on there it is doubtful Google will list that as a link because you are not getting much value from that site. It is still helpful but not shown in the backlink count.
However, if you have a link from a PR 5 with 10 outbound links you will show for that because you get a significan portion of PR value passed to your site.