Compare what number? Are you saying that an internal link from a page that is lower than PR4 will not show up in Google's link: search?
That was the case earlier today when, as you pointed out, Google was showing no inbound links yet a search for the link itself found a couple inbound links.
As of right now, Google's inbound links are showing for me, so the example no longer holds.
As far as the search link you provided what does that illustrate? I can see how it makes a lie out of my suggestion that Google doesn't know the site exists, but it does prove the site has a PR of 4 or better. In fact my toolbar doesn't give it any PR at all.
It's not the PR of the search results page on Google, but the PR of the listed pages that matters.
And you still haven't explained why a link: search on this URL yields nothing.
I think has been explained. Google doesn't show all inbound links to a site. However, as pointed out above, this particular example is now showing links while it wasn't earlier today (at least for me).
Maybe it is the mess that Google's PR ranking seem to be in at the moment, but I'm sure I can find you multiple instances of sites with PRs less than 4 being listed as in coming or backward links to pages by google.
I'm sure you could and we could spend a lot of time trying to analyze every exception.
At a high level, I hope people understand that (all other things being equal) a site with more inbound links will generally rank higher than a site with less inbound links. Since Google's inbound link report is somewhat abridged, don't rely on that to determine exactly where you stand vs. competing sites.