That's a good question about adcoms comparing the two applications. I really doubt that adcoms throw away applications very often, especially of those that they had interviewed. Alit of schools keep LOR's, DAT scores, and other supplemental stuff, so to say they have it and can compare the two isnt a very far stretch. However I dont think a huge change of the personal statement is necessary. It is not like in over the year you have totally changed as a person, so you shouldnt change the thing that says what kind of a person you are. That being said there is no harm in listing the improving factors on your application this cycle, and maybe listing why you applied again and how the first denial has strengthened you, made you better, or more determined.