Basically, C's semantics assume too little - everything is a primitive type or a pointer dressed up to look like something else. Pascal has a stronger notion of types and this allows for additional automatic optimization where they're relevant - memory layout just happens to be one such area.
I miss the ability to pair structures as "antagonistic" - aka if one exists the other is not, thus allowing for unions of various datatypes who guarantee that if they exist- the shared memory they reside in is theirs and theirs alone.
Just a wild guess: Pascal may use tightly packed structures without alignment by default?