Well they definitely use more UREA to reduce Nox emissions. VW was claiming 10,000 miles per tank of DEF and owners are reporting they were getting 15-20,000 miles. With the 6.7 under light duty use, we use 5 gallons every 6,300 miles or so and some are filling up every 3,000 miles if towing heavy. Granted you can't compare towing heavy to a VW so if you factor 6,300 miles per 5 gallons compared to VWs 15k-20k miles...
Not sure if that is a good comparison or not. You can say that the 6.7 is over 3 times the size of the 2.0 so it obviously will emit more which is why it uses more..