> When they have a monopoly, places like the EU will frown on purposefully breaking compatibility.

What exactly have they done about it?

Without knowing too much of the EU history, I have always understood that anti-trust pressure from the EU effectively forced Microsoft to publish the OOXML spec in the first place.

> Purposefully

According to who? With what proof? And how/why do they get to be the arbiters of that?

> According to who? With what proof?

They normally get asked to investigate by other interested parties, and then ask other independent experts in the field.

> And how/why do they get to be the arbiters of that?

By being the government?

Microsoft doesn't have to sell their software in Europe if they don't like the rules.