One of my favorite dessert recipes is Dorie Greenspan's French Apple Cake. It calls for "4 large apples". The recipe is equally enjoyable with a wide range of apple mass, but the character is definitely changed depending on what you do. I think baking is a lot more flexible than most folks give it credit for, but getting more precise units helps ensure consistency from cook to cook and from batch to batch.

For reference a friend who'd expatriated to the midwest posted something about some giant apples they bought. I replied with a picture of an average apple I bought, roughly twice the size of theirs.

  Meanwhile, the "cup" measurement can vary depending on the order of which you
  put the apricots into the cup - do you put the smallest fruit in first, or
  the biggest?

Sure, volumetric measurements for solids is generally not great which is why when I transcribe recipes for my own collection I tend to weigh things out.