Exactly. It reminds me a bit of this
Now, CIFS is pretty much just a serialization of NT I/O semantics over the wire (for some reason this surprises and confuses people from the UNIX/TCP camps. What do they expect?).
In the same way that CIFS aka SMB is a "serialization of NT I/O semantics over the wire", the .doc data formats are a serialization of Word's internal representation of a document. There's a lot of subtlety in that representation as he mentions. The Mac and Windows versions had different epochs, there's a whole bunch of things like "keep this paragraph with next" in the UI that need to be encoded in the file format. Also Office depends heavily on OLE (which was developed for Office) and thus OLE compound documents are part of the spec. They can include Windows Metafiles which are a serialization of GDI commands.
So you ended up with something that had a load of features and run fast on 80's and 90's machines with by current standards glacially slow CPUs and disks. It was cross platform in the sense that it worked on Windows and Mac. It was never really designed to be something that people outside Microsoft could reimplement easily. In fact I bet the original Mac version of Word wasn't intended to run on Windows - the point was to ship it on Mac.
Mind you I use OpenOffice on Windows these days and it seems like .doc and .xls files are now supported pretty well there. On Android Polaris Office seems to have no problems opening .xls files. Now the Open Office and Polaris Office teams must have spent ages getting this stuff to work, but it does. MS is still musing whether it should release Office on Android, but essentially the world has moved on without it.