Earlier quoted context omitted.
It's worth noting this is a testament to Microsoft's (extreme) dedication to backwards compatibility. I sometimes wonder who's more fanatical: the glibc folks or MS. But it seems to have paid off for both teams in the end, so (especially as a young engineer) who am I to judge?
This is especially noteworthy because the older Word formats were essentially memory dumps of the data structures used to store the document.
Individual data structures are then binary-serialized into that compound file, but I don't think it's accurate to call it a "memory dump". People often get that impression after looking at the compound file and seeing garbage there, much like unused blocks in memory - but that's because it's a filesystem, and as such, has a concept of unused "sectors". This is also why a freshly saved binary Word file might still contain bits and pieces of old data and metadata.