While submitting to a plethora of directories out their on internet, I found that some categories on the directory dont even have a single link, still their PR is like 5 or 6. How does a "almost" blank page receive such high Page Rank?
A category page does not need listings in order to have pr. 99% of the time the pr comes from the homepage, some directories send deep links to inner category pages which can make the page rank much higher in that category. If you find directories that have good pr on the inner pages but no listings then I recommend you take advantage of that and get listed in that category if your site is relevant of course. Doing so will give your site a higher pr boost since your site is likely to be the only listing on that page. Have a look at the directory in my sig, most inner pages have at least a pr 4 with very few listings which makes a listings in any category very valuable to your site.
deep link mean a link that is not at the main Top level. by the way, what determine the Page Rank is the INBOUND link. so even if the category does not have any link out, it still have a chance of having PR as it at least has one inbound link (the one from the main page)