Batman/DC Superheroes has been my fav theme since I was a child and reading that broke my heart, but I think you are right.
We had several DC superheroes sets and Im pretty sure the best sellers were only the ones with batman in it. The rest, despite some were awesome (like the Justice League Javelin 7, the brainiac attacks ship, or superhero girls school (yes, I really loved superhero girls too) didnt sell as LEGO expected.
To be fair, It can be taken as a joke, but really, everything with Batman in it is more popular. But putting Batman in EVERY set EVERY year can fatigue casual customers, and make sells drop too.
Hope LEGO dont let die the franchise...