Why wouldn't plain text suffice?
Why wouldn't plain text suffice?
Things like tax forms, license applications, instruction manuals, reports, plans, ...
Nobody wants to read or maintain ugly plaintext files. We don't even use plaintext in technical documentation, we use various markup languages, even if it's just ReST or Markdown.
E.g., see http://www.epa.gov/records1/faqs/rks.htm
OOXML, PDF, and ODF each have a standard "container" and key management model that makes this a whole lot easier than plain text.
7-bit ascii has been around for a lot longer than these formats which mostly represent a dump of the state of a formatting engine into something like XML in a file tree and compressed with PKZIP.
I'm not really familiar with the internals of ODF, but OOXML, while it does capture quite a lot of UI state, is actually quite clean and represents the intuitive document structure rather well.
http://orgmode.org/manual/OpenDocument-Text-export.html#Open...
is nearly always true. Provided X is actually possible.