It looks (to me) like people just stopped commenting on blog posts. More and more, I might find some great, very technical post, just to discover it has zero comments; ironically, I'd probably got there through a link on Hacker News or Reddit or G+, where it'd have dozens (if not hundreds) of comments. The original author might or might not know about the conversation; if it's happening on one of the large portals, he'll probably find out because of the traffic surge and its side-effects (db crash, bandwidth bill, etc), but if it's happening in a smaller community he doesn't participate in, he might remain completely oblivious to its existence.
This is a sad anti-pattern, exactly as bad as Disqus; it's just another way of building information silos. It's even more sad to see this model being pushed by the geek community, who should know better. Yes, trackback/pingback and RSS have failed; but there must be a better way to interlink the debate across this bunch of URLs we call "the web".