Diesel engines: better low-end torque?

The Germans are environmentally obsessed and Germany, on the whole, is the cleanest nation in the world. Cars with catalysts used to come with a bypass pipe so when you drove outside Germany and "bleifrei" wasn't available, you wouldn't ruin your Katalysator. When you got back home and ran out the leaded gas, you put the catalyst back. Everyone did, too. Now old cars must be retrofitted with catalysts, but, they have developed retrofitable EFI for many old cars. I have mixed feelings about this, but the thing is, it's being implemented consistently. It's like ULSD, if you are running a vintage Cummins or Cat you may have to refit the pump (not too bad on PT Cumminses but high dollar on Macks or Cats). What's good for the goose is good for the gander.