zabalex - 9:30 pm on Feb 28, 2012 (gmt 0)
In my opinion it should be PageRank, as google has always mentioned that it is in violation of the google TOS to manipulate the PageRank in anyway.
By turning that signal off google can be assured about there is no effect on SERP of a website if he managed to get some high PR links and also there will be no benefit to the websites inflating the PR by doing anything.
In many cases a back link from a low PR page is much more important than a back link from a high PR page. So evaluating the back link with respect to PageRank becomes irrelevant.