As has already been discussed ad nauseum, Apple is not bein irritating to get a "30% cut" (which is a bothersome way of describing it as they don't den get 30%: they get what is left over after paying you your 70% cut and then handling their numerous fixed costs with relation to selling your products): they want control over distribution. For more information, read this entire thread.

http://news.ycombinator.com/item?id=4037065

As for how you do it, in practice 99% of licensing schemes are based either on "serial number", "mac address", "license key given to user and typed into app", or a combination of such. While some people then can't import still, almost everyone can, and that is enough to be game-changing.

Note: you don't even need to allow this list to e changed after you import the product if you are still concerned about a "30% cut". (Though, Cydia does allow this, and even fully automates it by way of a backend licensing API vendors can implement to take control of the purchasing process, and in practice vendors that start using this mostly use it as a temporary measure and eventually just switch over entirely).

Apple doesn't care about the distribution of apps. Gatekeeper makes that abundantly clear. Please present a cogent argument that takes that under consideration.

Apple, however, doesn't want to be on the hook for maintaining and supporting and spending bandwidth on users who haven't given them a cent. I can't blame them. Again, I'd love to be granted the ability to bless "legacy users" into the Mac App Store, but I also don't understand why Apple has any incentive to ever allow me to do so. It costs them money and resources, with absolutely no benefit in return.

Why do you think they have an incentive?

And yet, they have all these free apps...

But it's still dirty and cumbersome and error-prone and they have to assign some staff to this thing... In Steve Jobs's word: "Yuch"!

That is not to say I wouldn't want this. I think it would be wonderful, but I wouldn't bet on it.