i personally dont really care about page rank because i am ranked 0 and am still on page 1 of yahoo msn and google for a couple of keywords like local sexy women, and a list of crap along those lines BUT I AM RANKED PR 0 SO I DONT REALLY CARE FOR IT TO MUCH
nothing is so prfect like human brain. the pr predictors are the software which are developed with a concept of prediction by keeping the current situation in mind. but the seo is dynamic by nature so the seo predictor can not be a perfect one.
expect what you have done and what should be your page rank. what ever expetation you have got is the perfect expectation