PCalc is a work of art. I can't personally speak to the developer's philosophy here, but it feels like they sat down and asked themselves how they could make the best possible app in this very specific domain, then doubled back and added an extra 10x attention to detail on top.
A calculator app might seem like a very small thing, but the availability of PCalc is literally one of the handful of items I have in my "pros/cons" list of using iPhone vs. an Android phone.