Just as a clarification: Why do they ask for a minimum word count (or space count for that matter) and not for a minimum quality of the content. If students can accomplish the same with less words, then so be it.
I once had a professor who assigned regular essays with a maximum length of one properly formatted page. He was quite demanding, and I think I probably learned more about writing from those than most other multi-page assignments. He was also probably the most brilliant professor I'd had.