The fact is that when the fabric is folded, as it is at every seam, something is lost in the seam itself. It would be impossible to design patterns that made up for those few threads. You would have directions that told you to cut 2.52 inches for one piece, and 1.77 inches for another, and you would never be able to measure that accurately. It's a lot easier to just learn to sew a scant 1/4".