I'm right there with you -- I had the same eureka moment when I took the class on draping the francaise with Janea Whitacre from Colonial Williamsburg. She stressed exactly the same thing -- they took a big piece of fabric and did whatever was necessary to make it work. It was really liberating watching her work! We draped right out of the fashion fabric; we put tucks where we needed tucks, adjusted seamlines where they were needed. She says she forbids her apprentices from using any sort of measuring device in her workshop, making them all use finger and handspans.

It was cool, b/c I'd already been moving there in my own sewing -- all of my seamlines are 1/2", and unless I'm drafting patterns I don't even bother to measure that anymore.