I imagine that a lot of folks are still getting used to the new format, and without the preview box, there does seem to be more perceptual “distance” between the websites and the forum. Before it felt like you were just navigating around within the same site, but now it feels like (what it is) leaving the forums to go to an altogether different internet location. Sure, it’s not really hard by any means to navigate from the forums to one of the network sites and back again, but it’s now pretty obvious that you’re leaving the forums to go look at something on one of the sites. Add to that that every link clicked on one of the new sites takes you just that much farther away from the forums. Before they essentially felt like one place, but now it’s clear that they’re totally different internet places.
It could be that there’s just some hesitation to do that (perhaps even an unconscious hesitation, at that). Leaving the forums might “feel” like leaving a comfortable and familiar place, like stepping out of a warm room full of people you’re socializing with to go into another room by yourself to look at something. Then, when you return, you’ve seen something but no one else back in the first room has shared that, so there’s less motivation to bring it up in discussion.
That is, the issue might be more about the psychology of the shared social experience of the forum place and less about the specifics of the way the notice about the new item is made. Perhaps the issue is the perception of the integration of the review-announcement article with the forum.
I don’t know what the technical remedy could be to increase the perception that the forum and the website(s) are a seamless whole, but perhaps that’s what needs to be changed?