M$ scores in Office due to its proprietary document formats. Does OO have access to the entire document format as M$ has? Once it enters the ODF arena, it could be evaluated better against OO. Same with all other graphics softwares that use closed restrictive formats.
Format for new version of Office is as open as it gets.
Its XML, zipped and renamed to docx etc. Full documentation is available on MSDN site. Even Office 2k , 2003 lets you use XML instead of native format.
-Shamit