Gruber seems to be mocking Adobe's claim by suggesting that Microsoft Office is more open.
However, he never explains why Microsoft Office is not "open" and seems to be counting on generic anti-Microsoft sentiment to make the case for him. His post may have been a lot more convincing if he had explained why Office isn't "open" and then went on to explain why Flash is less "open" than Office.
Btw I say all this as an developer who thinks that section 3.3.1 makes a lot of sense for Apple and as someone who thinks that Flash is too buggy.