Apparently Puyo's SD gag manga, which is being developed into a series of web shorts (along with the gag manga Nyoro~n Tsuruya-san), was given a significantly larger display than the main manga, and also had many more stacks of books-- in other words, the stores expect it to be a lot more popular than the manga.
Why do you think it is? My instinct is to suspect that it's because the manga, while good, is still a retread of the material from the novels, whereas Haruhi-chan is new content. (Not to mention the second volume apparently contains an eroge-loving Yuki. Why hasn't anyone licensed this manga here yet, again?)