Being locked into some vendor is one thing, but I find worse is people insisting to send something in .doc (or other rich text format) while plain text or texts in the body of E-mail would just suffice.
Though docx has its own problem -- a lot of free implementations do not handle it correctly and MS implementation of OpenDocument is largely incomplete (as far as I know from 2007's implementation...) Honestly, using LibreOffice day to day with other users being MS Office users, ironically doc seems to be most complete interchangeable format with these users.
I think some of those come from ambiguity of spec so I guess there are mulple parties to be blamed.