It depends on a number of factors, those sites that rank high could have been there for sometime, so the age counts, and ofcourse people are getting backlinks without making it obvious where they are getting their backlinks from
Because, backlinks is just one of the many factors considered by search engines in ranking a website. Maybe the site with more backlinks has less "quality and relevant ones" than the other site. remember that ranking isn't only about getting more backlinks...