Uh, don't agree with you on this one. I mean, it took Iron Man 3 four days to unlock the sneak peek of the trailer, on a FB site with over 10 million likes and people knew what they were unlocking so that's an added motivation! Besides, not everyone wants to share a TDKR add. I know quite a few people who wont out of principle. I did, even though TDKR was, for me, one of the biggest disappointments ever in terms of movies.
Not saying that there is no indifference, at this point before we even had a proper trailer or anything really, it's to be expected, but I don't think that is the reason for the slowdown. I also still believe WB might be controlling the pace, as I've mentioned in one of my previous posts.