The technical committee was specifically limited to producing a format that was a subset of a single vendor's own proprietary format.[4][7] 

 Its a valid crit, and definitly one that has been voiced. 

 : The same applies for OpenDocument. It is a critique you can voice on 99% of all standards as standards generally comprise of existing propriety stuff. Also OOXML is a superset of the original MS formats allthough not by a whole lot. Actually OpenDocument is a subset as they did not implement the formula's from the originating format.