There are two fundamentally different issues here: (1) Is highly reprehensible and Orwellian, (2) Is the perfectly normal and appropriate behavior of a business in a free market.
1) First is that Apple uses DRM to prevent apps from sources other than their own store from running on devices they have sold and no longer own. This is an Orwellian threat to basic freedoms, civil liberties and human rights. It is the reason that I am a very strong critic not only of Apple's business model, but more importantly of DRM (digital restrictions / rights management, technological protection measures, digital locks, copy protection etc.). I am also a even stronger critic of the oppressive actions of governments by using national laws and trade treaties to protect DRM. DRM is fundamentally what turns in this case the normal decision of what a business chooses out of their own free will to sell or not to sell in their store, (2) below, into a vehicle for Orwellian censorship and oppression. I have covered this issue in the following threads in particular as they relate to Apple's use of DRM to censor Dash:
https://bitcointalk.org/index.php?topic=1617815.0;allhttps://bitcointalk.org/index.php?topic=1369389.0;all2) Why Apple may sell or distribute apps that support certain crypto currencies in their store. Selling or distributing anything implies a form of endorsement so there is obviously a form of endorsement of certain crypto currencies here. One possible theory that has been proposed is based upon my following post:
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1) Regulatory compliance.
This is the elephant in the room in crypto currency and Monero is one of very few crypto currencies that has avoided some very serious regulatory compliance risks. The critical aspect of this is the guidance that was issued by FinCEN in March of 2013.
https://www.fincen.gov/sites/default/files/shared/FIN-2013-G001.pdf. In order for a crypto currency to be compliant while at the same time avoiding the requirement of registration as a Money Services Business, and consequential AML/KNC requirements, the crypto currency must qualify as a "De Centralized Virtual Currency" under the guidance. This means that the block rewards have to go in their entirety to the miners and cannot be diverted for other purposes such as to fund development or marketing. If the block rewards are diverted in such a manner then those who are administering the diverted block rewards would be very likely be considered to be "administrators" or "exchangers" under the guidance, be required to register as MSBs and be subject to AML/KNC reporting requirements among other requirements. Ripple has already been subject to regulatory enforcement over this very issue. While I am not aware, at this time, of any regulatory action over this against Dash, the risk in that case likely remains very high. While this is specific to the United States, the reality is that the United States is at least for the time being, the world leader in financial regulation in particular because of the reserve currency status of the United States dollar.
In summary one needs to keep one's hands out of the till, block rewards, in order to keep the regulator away.
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If we consider the initial "allowed six" Bitcoin, Litecoin, Dogecoin, Ripple, Ethereum, The DAO, and now Monero the FinCEN theory is somewhat plausible as follows;
1) Bitcoin, Litecoin, Dogecoin and Monero would qualify under the FinCEN guidance as "De Centralized Virtual Currencies"
2) Ripple would qualify as "Centralized Virtual Currency" that has settled with FinCEN and become an MSB.
3) This leaves Ethereum and The DAO. Ethereum normally would not qualify as a "De Centralized Virtual Currency" because of the initial sale of Ether for Bitcoin would make the promoter of the initial Ether sale and MSB as an exchanger. There is in this case a loophole in than an MSB is not required to register until after six months. In the Ether case this MSB promptly dissolved after the initial sale effectively possibly avoiding the MSB registration requirement. This is the kind of legal loophole that companies such as Apple use all the time. Whether it turns out to be legal in the end is beside the point; what matters in the case is that Apple is comfortable with it. As for the DAO it was not around long enough to trigger the MSB registration requirement.
So there we have just a possible theory for those who wish to attempt to reverse engineer Apple's store vetting process.
Edit: I should make it clear that business should always have the right to choose what to sell or distribute in its own store, it is the use of DRM to block other stores that is the real issue with Apple.