PR 5 or PR 0

[iBizStart]

PR 0 seems more like it but I checked the google PR for my site:
www.seekster.com came up as PR 5 but
seekster.com came up as PR 0

Any explanation?

 

[.com.net.org]

they're treated as their own domain.
www.seekster.com is a domain
seekster.com is a domain
subdomain.seekster.com is a domain

Also it's called Page Rank.
So it's actually based on PAGE not domain nor subdomain. (above explanation is a bit wrong but maybe simpler to understand).