Matt Cutts recently spoke with Rand Fishkin of SEOmoz and made a few interesting statements that elicited some interesting forum response.
First, WebmasterWorld members were particularly interested in this statement:
we did do a full PageRank update several weeks ago - there's less PageRank flowing around in some areas (e.g. search and SEO). Vanessa Fox's site dropped by one as well, and for her as well, it's just a case where less PageRank is flowing in some niches of the net. PageRank doesn't always monotonically increase.
The forum member asks if Google is being selective in key vertical markets.
Well, this is news. At first, we were all concerned about the attack on paid links since Google is clearly declaring war on paid links. The suspicion that more popular niches get negatively affected is a whole new ballgame.
So this could be related to a "balance of popularity" as one member puts it.
If some areas gain in overall link share, or entirely new segments are introduced (with some hype) they will be calculated into or even become (or come closer to be considered ) the new scale, the new meaning of PR 1, 5, 10.
Which means all the people who were saying that PageRank 4 is the new PageRank 5 were right.
To say "page A shouldn't rank at this position because it has paid links" commits the logical fallacy that it's the paid links that cause page A to rank, as opposed to the other links to page A.
In other words, just because a site is buying links does not mean that it shouldn't rank well.
The discussion goes on to suggest that those who sell links are the only ones who will really be penalized from this, but not those who buy links. As another member puts it, Google is so dependent on backlinks that this is a "fear" tactic to prevent this.