I don't know why this happened. Maybe it was just dumb luck...
I recently redesigned one of my websites that had PR 0. It was html with no CSS like the old days. I pretty much just slapped it together with frontpage (Yeah, I still have frontpage) all sloppy, uploaded it, built a few links and let it go. To my surprise it went up in the SERPs to page three of a high competition keyword within a couple weeks. I redesigned it using microformats and css, but used the same meta, content etc... I also tried to make sure it had a good woorank. When it got crawled, it ended up with PR 4. Went up in the SERPs a little. Been working on another site to see if it was just dumb luck. It's currently a wordpress site and I've never had any luck with PR and wordpress no matter the quality of links I build.