That is good but the wording of the assignment in one case places the emphasis on the presence of the content and not on the quality.
Whenever I am allowed, I note in the grading rubrics that the quality of a post must pass a test of "substantive" I simply do not count a post or message if it is not substantitive. I try to avoid evaulating the quality of the content and make a test of all points or no points.
Result? the students spend more effort in raising the quality of their post..and do more than sometimes I expect.... for which I do not complain.