The author doesn't get it.
"First, Microsoft does not support Open Document Files (ODF), a rival ISO file format standard used in OpenOffice, among others."
ODF stands for Open Document *Format*. It is not a "rival" standard; it is the *incumbent* standard.
"Second, many in the anti-camp are against OOXML - because they are against Microsoft."
Not the main reason. The author should have consulted somebody knowledgeable, somebody qualified to comment on the subject.
"But considering the efforts made by both sides, it must be very a important game, mustn't it?"
The name of the game is open standards (with multiple deployed implementations) versus vendor lockin (with *no* conforming implementations).