In extremely competitive situations, the slightest edge matter. Arguably test prep is less of an edge than spending a summer on some community project would be but even a relatively small point jump is an edge for someone on the bubble. And, of course, elite schools have become hyper-competitive. I have very few illusions that I would have the school choice I had when I went to college--especially given that that about an eighth of my class went to the school in question.
The real problem [edit: with scores] here is that scores are reported on a 200-800 scale. If they were reported in terms of standard deviation from the mean, then those 20-40 point differences wouldn't matter to admissions officers. As it is, a 30 point difference looks significant, even though it's only around 0.15 SD.
I'd hope that admissions officers are sophisticated enough to know that. Having said, there's some band in which you're basically flipping coins given overall criteria so you flip coins based on statistically insignificant numbers rather than complete random number generators.
In extremely competitive situations, the slightest edge matter. Arguably test prep is less of an edge than spending a summer on some community project would be but even a relatively small point jump is an edge for someone on the bubble. And, of course, elite schools have become hyper-competitive. I have very few illusions that I would have the school choice I had when I went to college--especially given that that about an eighth of my class went to the school in question.