The pages cited by Bruce are not the feeds themselves, but rather pages that contain provide for access to the feeds.
The first one,
http://blog.nikonians.org/index.xml, uses iPod podcasts to broadcast content, as shown by the following source code from that page.
Code:
<rss xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd" version="2.0">
<channel>
<title>Nikonians News - Photography & Imaging News and Podcasts</title>
<link>http://blog.nikonians.org/</link>
<description>Nikonians - The Worldwide Home for Nikon Photographers - Photo News & Podcasts</description>
<language>en</language>
<copyright>Copyright 2012</copyright>
<lastBuildDate>Tue, 31 Jul 2012 01:21:26 +0100</lastBuildDate>
<generator>http://www.movabletype.org/?v=4.1</generator>
<docs>http://blogs.law.harvard.edu/tech/rss</docs>
<itunes:new-feed-url>http://podcasts.nikonians.org/index.xml</itunes:new-feed-url>
The actual feed source is
http://podcasts.nikonians.org/index.xml, as shown in the last line of the above code.
While the page cited by Bruce,
http://blog.nikonians.org/index.xml, does indeed have a
TBPR of 4, the actual feed,
http://podcasts.nikonians.org/index.xml has only
TBPR 3.
That this particular feed has
PR owes, not to its URL being on the page cited by Bruce - its presence there is not in the form of hyperlink, i.e. it is not an actionable link, and therefore does not count for
PR purposes - but by virtue of it's being publicly accessible and having been discovered by others, so that they may in fact link directly to it. This is not necessarily the case for all feeds.
So, to clarify, and is evident from a close reading of this article, Bruce was speaking of the
PR that the page that provides access to the feed, not to the feed itself.