I've also done some work dealing with the Excel file format for a personal project (.xls not .xlsx). I think it needs to be clarified (not that you're implying

I've also done some work dealing with the Excel file format for a personal project (.xls not .xlsx). I think it needs to be clarified (not that you're implying this), that at least a lot of this mess isn't deliberate obfuscation on Microsoft's part. For instance the SharedStringTable is something that made a lot of sense when documents had to fit on floppy disks. Excel is 26 years old, a when you evolve the file format for as long, while trying to maintain backwards compatibility, you'll inevitably be stuck with a messy format.