* That would basically open the door to insanely easy piracy. Like on Android.
* A fairly nebulous and meaningful requirement
* I don't think it is an algorithm.
This is an awful argument.
Those who are going to pirate apps have the means and skills to do so. Even on the precious iPhone. Yes, you are able to pirate Android apps quite easily as a lay person.
An intermediate approach would be a system where binaries distributed exclusively via the App Store could (enforced using the same kind of signature system presently used) only be installed via the App Store.
Give developers a choice rather than making it for them.
* Even the Copyright Office has implemented DMCA exceptions for 'jailbreaking' to run legally owned/leased software which may not be available on, or restricted by, the 'official' sources. So even the curators of the DMCA recognize this requirement.
* Many times you cannot even successfully search for an App BY ITS UNIQUE NAME. That's just entirely and incompetently broken. Know who gets search right? Torrent sites and eMule. I can sooner find what I'm looking for there than on either Apple's, Google's, or Microsoft's App stores. And if these channels can do it, so can the majors.
No, it's obvious the majors all consider their App stores 'good enough', and since they can lock users into their services and out of others (both through technical barriers and unenforceable claims), there's no incentive for improvement. In fact, things have and (I suspect) will continue to get WORSE.