They would need to be able to scrutinise then change Apple's appstore approval process/policy and make sure that it is indeed being followed. Apart from affecting their macro policies, this precludes that Apple's ability to decide arbitrarily which is pretty important to what they are trying to do. If you do take a more general/macro view, which I think you need to, you need to take into account how this affects Apple's behaviour and the general effect on the market.
The idea that apps need to be babysat and approved is controversial, but worth testing. This is what APple is doing right now, in the market. They are testing a hypothesis: 'An authoritarian marketplace will result in better apps and a better user experience.' Other hypothesis such as: 'some babaysitting is good but we should let people opt out and install whatever they want' will also probably be tested.
I doubt you would suggest the US should get rid of the FDA. It is not such a jump to conclude that if drug companies must be watched for practices which damage consumers, why not a retail firm? The line America has drawn for regulation is just as arbitrary as the one European countries do, Europe is just a bit more suspicious of laissez-faire capitalism than America.
And I highly doubt they are baby sitting this app because of quality.
To put all this in context, I was responding to a comment that could be paraphrased 'Most of us agree what Apple is doing sucks, European (Commission?) should make them do it differently. The only reasons not to are some hazy moral theories I don't believe in.' I was talking about some of the practical reasons not to, the costs. One of those is rule of law.
Food, medicine, narcotics, etc. all these regimes also require relatively arbitrary regulatory powers too. That is also not good for rule of law. We make tradeoffs. Purer, direct democracy for stronger institutions. Rule of law of regulations. Laws for liberty. Each of these has a cost. Sometimes it's worth it.
Maybe regulating the appstore is a good idea. I don't think so. I'm trying to argue that the costs typical to this kind of a decision are high hear while the gains are low, perhaps nonexistent.
BTW, I don't think that Thingie was being unreasonable either. Like he says, the current reality is that it is not that crucial to find the best way of getting iphone apps.
So open would mean "if Apple was forced to lower the demands on the applications submitted to the app store" in this case, I guess? To which I would say, "Quite the contrary." I think Apple should enforce higher requirements when it comes to human interface guidelines, for instance. But it's of course a process that's evolving, and it will take some time to get it right.
One could argue that the demands put on the Apps in the App store is increasing competition, since it encourages developers not wanting to be subjected to them to develop for alternate platforms. I just hope the courts will see it that way, if it comes to it.