The difference is that the government has put in place systems to deal with these higher polluting vehicles. It taxes them more, to discourage people from owning them. By lying about the pollution levels, the engineers are encouraging people to own more polluting engines. Not only is this obviously unethical since it involves lying with the purpose of breaking a law, but this law also happens to be designed to try and reduce the deadly effects of pollution. So such behaviour is, I say again, obviously indirectly linked to more people dying.