It's not just cracked apps. From the developer standpoint they want to be able to ensure that as many customers as possible are using the latest version of their app. There's security and feature concerns when they have to deal with multiple versions across the spread of handsets. That's the core of the fragmentation problem Android is battling with atm. So.. Apple take a pro-developer stance; again it's either/or. You have to make a decision one way or the other.
As a developer it honestly doesn't concern me that much, I took the decision a long time back to not support anything but the latest SDK for obvious reasons: new feature support + because it indirectly stems the tide of usage from JBs (JBs are usually a version or 2 behind)
Also given the option to upgrade at no cost, most customers automatically apply upgrades anyway, encouraged along by Apple's fairly consistent reminders.
Android's problem is more endemic to the complexity behind the scenes of the Android update process i.e. Split of responsibilities between Google, the OEMs, the network provider testing, the huge array of devices, ...
Apple's upgrade path works better, simply because there's less devices and they've assumed full responsibility for everything.
So theoretically if Samsung chose to branch off its own version of Android, incl. replacing the Google extension framework & apps, its feasible to believe they could similarly replicate Apple's up to date model.
The problem however in practice is not so easy to achieve as Google has recently started to incorporate more of Android's new core SDK functionality only under its proprietary licensed extensions framework as opposed to including this in the open source part of Android, essentially making future breakaways unfeasible. I.e. Their recent moves are a clear indication that they don't want more Amazons, hence Android today is far more locked in for OEMs than of yesteryears. Also to note is that the terms & conditions for use of their proprietary extensions, specifically restricts branching off.