Windows Mobile has not had the ability to handle OOXML-based documents until now.
This might make 2 applications which are built from the same codebase and properly support a derivate of OOXML. Both applications come from the same company, to whom OOXML is "a simple matter of (its) commercial interests", according to its own manager.
The commercial exploitation of users won't stop until users exercise full control over their software or - more broadly - their computing (including data)