Ok, why do people always think that their traffic is going to increase once the PR update is done? Imagine a fence between us and google. The PR of your site will change to whatever on google's side depending on what backlinks you have at any time. Now, it would be stupid for them to update all datacenters when your PR changed, so they just do it a few times a year. The number you see is just a reference number and won't change your ranking once it updates. Plus it is quality backlinks (including high PR ones) to your site that with give you a boost in rankings. The change your SERPs happens as google indexes the sites which have the backlinks to your site.
Well your mostly correct.... But lets jump out of the box here for a second. Say we own a directory that gets PR8 from an update. That WILL increase traffic because more people are going to go to the site now and more sites will link to it bringing in more traffic and better SERPs. I know what you are saying but just bringing this up for the sake of argument.
but you underminded your argument in what you said you said that more visitors will link to it - the backlinks will increase the rankings. What you say about a directory being more popular because of a PR8 may be a one off difference because high PR backlinks is what they are there for. BUT! 1) no one is going to know it has PR8 unless it is high in the serps anyway, then people will start linking to it, pusing it up the rankings 2) to get PR 8 in the first place you would have to have a lot of backlinks, so be near the top anyway.
If a new PR8 directory came out from this update the word would spread fast and it would spread by links. Remember you have a ton of dedicated people that when an update happens they will go out and check every directory they have their link on. These are the people that will notice the PR change and spread the word. But without all the details... Your thread says "PR update does not mean change in traffic" and I think we can both agree it depends on your site. Meaning it WILL change for directories.
Ok, I will add a word to it "SERP" traffic meaning the specific keyword it is usually found in google under. Rather than referal links from forums, bookmark sites, etc...