The top-end students are least likely to need additional resources to keep them on track academically. For non-academic factors, the biggest advantage at some highly selective schools is better financial aid, but prospective students comparing admission offers should be able to compare financial aid and net prices that accompany them.
Really, it looks like college graduation rates show mostly a selection effect (i.e. how strong the students who get admitted are) with only small treatment effects (i.e. what the college does that causes its graduation rates to be higher or lower than those with similar strength students) in most cases.