I'm not saying this is the only reason for the lack of warm up (especially today), but it was a significant part of the perceived reduction from old diesels. It's also why if you put petrol in the car by mistake, you can still ruin the engine even before you've turned the ignition (as opening the door starts the warm up and fuel pumps etc)
Modern car aren't actually completely on or off when you turn the key, sure. However I've put petrol by mistake in a diesel car twice and didn't ruin anything (but lost some money cleaning the mess up).
