Links below site level two doesn’t exist – Most search engines index only content in the top levels of your website. They have no idea that links exist beyond the secondary level simply because that they does not search beyond the secondary level. In other words, 5000 links pointing at your website, but all of them exist on pages beyond the second directory level, a search engine will determine that your website has zero links.

Email links can not be counted – Users have spend more time using email than they do surfing the web.

Free for Alls, Spoofers, and Link Schemes abound – Any time the search engine comes up with a new way to rank pages, someone has comes up with a way to trick the search engine.

Unauthorized URL has submitted to search engines – When the search engine folks first have decided to count links, I don’t think that they ever thought it would inspire people to begin submitting more links than they ever had, including other people’s pages.