We'll never know, because Microsoft settled before EU was able to do a full investigation of the company's business practices.
Of course we know the answer to that question, your deflection is a fail. The answer is MS never prevented anyone from installing any browser of their own choice. Only people that don't know anything about computers would think otherwise.
What did happen though was that Opera wasn't getting marketshare because of a broken business model. They then ran to the EC and somehow convinced them that the reason they failed was because somehow MS wasn't giving users a choice. The EC bought this bullcrap hook line and sinker and then forced MS to give users this "choice" that the evil MS previously prevented users from making.
The fact that EC could be confused between lack of choice and lack of marketing is sad and scary at the same time. I guess with a bunch of computer illiterates it probably isn't such a big surprise, and given the fact that the possibility of extorting such huge amounts of money must have wiped out any remaining sense.