I've been testing to proof myself whether this theory is true or not. Rather thank asking you guys, I think it's better if I tried it myself. So, in the past few months, I've built a backlinks to my new money making site..which is currently making me money..with www and without www but most of it with www.. if I did it the same than there is no difference right.. So, here comes the result..my site that I use to backlinking with www have a PR4 Backlinks without www gave me a PR 1 result.. So, for me this theory is true..from now on..STICK to only one. REMEMBER, if you use www, make sure you use it to all of your backlinking strategy.. I hope this helps..