Okay, I thought it would have been quite clear but I guess I'll have to explain it. The object of not buying the domains was to ensure that they were no other influencing factors in the PR other than the links I created six weeks before. I was NOT suggesting that you don't buy the domain until you've had links for six weeks - I only did it for the purposes of the experiment.
Are you confusing PR (PageRank - the google green bar) and PR (Page Rank the ranking you have on the search engine results page)?
But yes, I agree that Brett's advice of not placing a site on the web until it's ready is good advice from a user point of view - BUT Google has created some sort of (useless) Sandbox and this forces webmasters to find ways around it.
Apparently Sandbox is supposed to weed out auto-generated spam pages or something but it is just NOT WORKING, all it does is make Google look stale! (Sorry, I had to shout that but Google are a little too interested in IPO right now to hear about their search engine.)