This is a problem that I have observed for years. There is a lot of history to it, with lots of high profile examples, some very blatant.
Here is a current example that is happening right now...
There is pagerank 9 site with hidden links using the <no script> tag. The site with the link was registered in January and has a pagerank of 8, and is in turn linking to other sites in the body of the page, and those sites have a pagerank of 6.
I know for sure that more than one person has reported this. There is even a youtube video circulating about it. Yet, these sites still have their high pagerank.
As time passes, if this example is like most of the others, these sites are now selling the links to the highest bidder. In essence, people who are not playing by the rules are making thousands of dollars, and outranking competitors that are running a much more ethical business.
Sure, they will be caught eventually, but in the meantime they are earning money toward their next venture, and providing an example that the techniques work, and that thousands of dollars can be paid.
I've seen pagerank 8+ sites every single year for the last 5+ years get their pagerank using methods like this, andthe real problem is the sites receiving the pagerank keep it for months on end.
I don't understand the logic of receiving these reports and doing nothing the visible pagerank, allowing thousands of dollars to change hands as people buy and sell pagerank. Why does this problem keep happening every year?