Now, I'm too tired and/or lazy to crunch numbers tonight, but if you look at the overall volume of comments per week, you'd see a definite downward trend. If you take some of the more popular journals, like Stompy's, Washu's, EDI's, and others, you'll notice that recent entries don't have many comments anymore.
Another observation is first-post comments - in some of the journals there aren't even any first-post comments! Seriously! What the hell has happened? I remember ever journal getting 10+ comments and obligatory rate++'s for donating to our wonderful site, but these days I hardly see any of that.
I'm not trying to start a new omfg journal movement or anything, far from it. But personally, I'm going to try to comment in other people's journals more, and encourage everyone else to do the same. From a writer's perspective, comments are an enjoyably way to reap benefits from your work, and to gain constructive criticisms on your current projects.
So please, think of the kittens.