That article is too riddle errors to be great. Consider his paragraph on OOXML. He says that ODF does the same work as OOXML in 1/10th the size.
First of all, it does not do the same work. OOXML includes hundreds of pages covering spreadsheet formulas, giving mathematical definitions of them, sample input and output, and detailed descriptions. ODF omits spreadsheet formulas. ODF, as passed by ISO, barely deserves to be called a "specification", as there is virtually no chance that two people independently implementing from the spec alone would come up with interoperable documents. It is more accurately thought of as a guide to help understand the OpenOffice source code--which is what you actually would use as your spec if you were trying to write a real-world ODF application.
Second, even for those areas where they do the same work, the OOXML spec is more precise. That accounts for much of its size. For instance, consider how dates should be stored. Both ODF and OOXML list specific calendars that must be supported. In the ODF spec, this is a simple list, just giving a short informal name for each. In the OOXML spec, they give a table that gives the short informal name, but also gives the full official name, along with a complete citation to the official definition of that calendar.
Or consider password protected documents. All ODF tells you is where to store the password. (It might also say it should be hashed). OOXML covers that, but also tells you what hash formats and encryption systems must be supported, and for each of those cites the appropriate standard.