Many journals in psychology feature articles of different lengths, often labelled as "brief report" (4000 words) vs. "regular article" (12000 words). Are shorter articles generally considered as equally valuable and important as long articles, i.e., do they count as a "full" publication in the field of psychology?
I think this will depend completely on who's doing the "counting". For purposes of faculty evaluation, tenure, promotion, etc, different departments may have different rules, so there won't be any general answer.
One would like to think that each article would be evaluated on its signficance, rather than length, and that decisions would be made based on overall contribution to the field, rather than a number of papers. Of course, this doesn't always happen.