If you see this blog http://networkusi.com/ you can notice that its PR is 3 but there is almost no stuff in that blog. So how can they get PR3 with almost blank blog.
I ran it through a pagerank tool that I am currently developing, and if my tool is correct, the domain is very old. I would be willing to bet that the domain probally had much more content and that the new owner did not earn that rank, they bought it in a sense. I hope that clears things up a bit.