Why some websites doesnt open with WWW but they open with WWW.

Why some websites doesnt open with WWW but they open with WWW like http://ift.tt/znRkhg http://ift.tt/1klAxK8

Few reasons i read are like this states that all traffic is routed though their primary website, does it mean there is no way to access a website through their http://ift.tt/2mbvhlY form?