FYI, I have both a Waterford built and Taiwan built Riv. I have one of the first run Waterford Hunqapillar frames and that convinced me to buy a Hillborne from a Taiwan shipment. Both are Rivendells. It's their lugs, their geo, their choice of tubes and specs. I cannot find any difference in the quality of workmanship or performance between the two. Looking at things from a business owners perspective, I assume Grant uses Waterford because they are set up for small production runs and his orders fit into the queue. The Taiwan factory requires minimum orders and more expensive inventory management. They are what they are and do what they do; make beautiful, comfortable and useful bikes.
Marc