I had one of my sails made without sewing the bolt rope at the bottom. In fact, I had the sailmaker leave a few spare inches hanging out. It was the best sail I've owned. The sailmaker wasn't keen and thought I was mad.
You are right Dave IMHO, it's the sail you want to stretch down not the rope and I too wonder why they sew them. Maybe because the uninitiated buy a new sail when they can no longer get the shape they want with the tight bolt rope. Naa too cynical <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />