Grip safeties are different, ejection ports are lowered and beveled, safety is different, and sights on most of the "defense" guns are different. Many also have a full length guide rod.
The 1911 that troops carried in the World Wars versus a new Dan Wesson is a lot like my father's 1932 Ford coupe hot rod. Still looks the same, but it has been heavily modified for increased performance in several areas despite it's relatively stock body.