Whats the Deal With PR Blog Comments

I've not been in this game long enough to know about blog comment spamming. However, when analyzing a competitors backlinks I'm seeing their highest PR link is from a blog comment. PR4. Of course everyone on this page is spamming the shit out of the comment section with their naked urls in the text fields. Clearly no moderation here.

But, why do people do this on an non-relevant blogs and want these links to their niche? Are they still living in the past or does that PR4 link that i'm seeing in spyglass actually count as a pr4 link? It a pr4 but its not-relevant, no-follow and a comment. What is the logic here?

It's easy to do. Does it work? Not in my testing, but that won't stop people from selling a PR 4 link to unsuspecting new SEO's and webmasters.

Could be commenting to trick you out in beleiving that's the reason he is ranking, meanwhile he might be building some links from his network and blocking the link discovery tools.