wheel - 11:51 pm on May 31, 2010 (gmt 0)

I have sites that I have removed all content from (years ago) - that retain their PR to this day. Anyone care to explain that if maintaining content and link structure is so critical?

Who said maintaining content or site structure has anything to do with PR? It clearly doesn't, so what you just described is 'working as expected'.

When you trash a site and the PR goes to 0, that's Google changing the PR calc - that's the exception. They've decided that outside the PR calc your site should go to 0.