tedster - 7:27 pm on Nov 4, 2011 (gmt 0)
Here's another factor. Google has modified the actual math for PR many times and those changes are not communicated in detail. One clear example is that PageRank started with a "random" surfer model, but has evolved into an "intelligent" surfer model.
In other words, when it comes to PR calculation, all links are not weighted equally these days - although in the original paper they were.