The curve is a convex edge. The shape provides lower surface area at the point of impact, increasing the surface pressure with the same impact force compared to a straight edge.

the baseline looks close to being a "sharp edge"...

really though, with the "New Book called "What if? 2" by the XKCD creator, can I get him to sign it? given the previous books suggestion: a cure for the common cold, "If everyone on the planet stayed away from each other for a couple of weeks, wouldn't the common cold be wiped out?"? https://news.ycombinator.com/item?id=30139925