The thing is if you sell a device running your software, there's no law that says you have to build in features and support for anyone else to install their own software. Feature phones are also computers, but there's no mandatory regulation compelling vendors to allow installation of third party software. Going a step further, if you sold a device with a proprietary only app store, so it can only run software you provided access to, like a feature phone where some features could be downloaded, again what's wrong with that? You used to be able to buy children's computers with limited educational software you could download, probably still can. Would you compel the vendor to open up that 'app store'? Chances are such a regulation would kill products like that stone dead. Same with consoles. Any regulation you make for the App Store should really count against consoles too, wrecking their whole business model.

It's like a slippery slope. If you enforce rules that say Apple must allow side-loading of software, doesn't that mean any computer should provide that facility? What if that opens up real security risks, is it really regulator's jobs to open up vulnerabilities like that? It's a massive, horrible can of worms. At the end of the day, if you want an open platform like that you can build or buy one. There's really no benefit to the market to mandate that all platforms must be like that though. If open really is better, then it should win on it's own terms not through regulatory fiat.