I've also def noticed a drop in comments.
It may be a page layout thing. I think the comments are too low on the page. Under the article you have the tags then under that, "share the news", then "related games", then the button for prev/next article, then "further reading", and then finally the comments. To me it seems too deep; people might just get to the end of the article, see arrows pointing to the next article and think that's it and just go to another page and miss the comments.
I already forget what the news article layout was like in 2.0 (lol), but I seem to remember the comments being closer to the article, so there wasn't much scrolling down to read comments.
As for your other question, I mainly stay on the hub page. When i go into a news article or forum thread, I generally just click "back" or click the hub button at the top. Once in a while I'll go into gamrfeed if there are a lot of new items. Don't really go into gamr connect. I like the hot topics on the hub page.