> why should both have the same PR...
Well I dunno but the subdomains are usually used for seperate pages whereas domain.com and
www.domain.com usually link to exactly the same page.
If Google treats them differently, then it could be inaccurately assessing the popularity of sites across the web because of the different ways in which urls are promoted.
Afterall, Google only tends to list a site as domain.com or
www.domain.com and not usually both.