You know, for someone claiming to be familiar with software packages, incremental updates and software engineering, as well as having common sense, you are not putting up very good or solid arguments. I won't bother to quote all your posts, this particular one will suffice just fine.
Please enlighten us - What exactly did you intend to achieve by comparing the two IPSW files? Or even the DMG files?
To borrow some of your terminology and put it to new use: If you knew the first thing about what you are talking about, your common sense would have told you that there is no point in comparing compressed and encrypted files like you did...