Oh yeah, that's why they do it this way. See, it does make sense.
If you look at this page, and scroll down to the section that is headed by "WHY IS APPIC DOING THINGS THIS WAY?" there's an explanation.
Basically, it's just to allow a buffer of time for those who didn't place to prepare themselves for the Clearinghouse process, without allowing internship sites to do illicit cherrypicking of unselected candidates beforehand.