I would assume it also depends on the emissions and fuel regulations in the country. The US has always had shitty diesel fuel at the pumps and it wasn't until around 10 years ago that you ultra-low sulfur diesel was ubiquitous everywhere. The 500ppm low sulfur diesel would screw up the catalysts. So the US answer was always to de-tune the vehicles, Germany had better configurations due to what I assume were higher fuel quality standards and less stringent emissions. Oh, I found a source confirming my suspicion: http://www.europarl.europa.eu/RegData/etudes/STUD/2016/58733... check page 16 for an overview.