[macspoofing]

I understand your point, but this is the reality of modern aviation. New engines are released for existing airframes. In this case though, it wasn't an existing airframe. This was a new model built around new engines. Where the analogy starts to break down is that unlike putting new tires on, any face-lift that is done to an airliner is backed by testing and and under the watchful eye of multitudes of regulators.