The most important aspect that defines the rank of a site is how much it is linked with other sites. This is very true if you look into details of the number of site being linking in with top ranking site. I have done a little research and to prove this theory.
Google.com - Rank no. 1 - site linking in : 656,011
Facebook.com - Rank no. 4 - site linking in : 258,619
aweber.com - rank no.255 - site linking in : 3,474
prweb.com - rank 4,507 - site linking in : 16,751
marketingtips.com - rank 21,507 - site linking in : 3,528
courtneytuttle.com - rank 31,583 - site linking in : 1,909
make money related blog - rank 157,954 - site linking in : 337
timelessprecisionwatch.com - rank 12,667,277 - site linking in : 2
You can see from the rank numbers and numbers of site linking in to it as proof.
Certainly, this answers Why is it important to build backlink. Good pageRank will do you good in getting first page on google or other search engine. so, go do article marketing and buy Angela's packet!
As written in http://www.warriorforum.com/main-internet-marketing-discussion-forum/96297-traffic-rank-relation-site-linking-proof.html#post905538