Why are people still so foolish that they mention PR in their trade request titles?

[Licker4U]

Originally Posted by Bill

Don't you realize that trading links based on PR is specifically against google guidelines, and is one of the likely sources of the current collapse of adult sites in google.

I'm only asking here because I want to know more, but how is it against Google guidelines? The only mention of link trades at Google's Webmaster Help Center is this:

"Don't participate in link schemes designed to increase your site's ranking or PageRank. In particular, avoid links to web spammers or "bad neighborhoods" on the web, as your own ranking may be affected adversely by those links. "

I find it hard to believe that mentioning PR in a post title would be considered a link scheme.