Do all URLs pass PageRank? No. Many affiliate URLs go through several redirects in order to get to the destination page. For example, you sell a product and start an affiliate program. People who sign up on the affiliate program want to do their tracking, where you want to do your own tracking.
So when they put a link on their Web site, they might use a URL such as http://www.affiliatesite.com/affiliate.php?referralid=232, which then might get passed through a 3rd party affiliate tracking system, so the URL changes to www.thirdpartyaffiliatetracking.com/affiliate.asp?affiliateid=234&referrurl=5832. Now you want to track the click coming in and if there is a sale, so you set up your own URL you asked them to link to, such as www.mysite.com/affiliate.jsp?affiliateid=232.
So the chances of PageRank being distributed to the main site (i.e. www.mysite.com) is unlikely. There are too many redirects.