I would argue that the target audience of the app store isn't tech-savvy enough to do this anyway. Sure, it's easy to HN readers, but to the general public it probably "sounds too hard."
The clunkiness of the iOS store has to play at least a part. Compared to using a music player on your computer, Cydia is a pretty user-friendly and elegant way to install applications.
I'm not sure if I misunderstood your comment. But as far as I know most iOS users install apps using the app store built into the device. It's really not much different, if not more polished than the cydia store.
I think the real reason for the popularity of cydia is that 1) it has a user friendly UI 2) you can get apps on it that will not make it to the app store and 3) some people are just too cheap to pay for some apps and use it to pirate them
The target audience of what? The app store? Each app? In Apple's eyes, their target audience is the entire computing population ... and it's not a stretch to think that an exploit like this will be simplified for the masses now that it's been identified.
I'm sure Apple will tighten it up a bit but if it stops casual piracy that's probably good enough. More sophisticated and invasive DRM schemes don't stop people anyway. It's a waste of time to go much further than "keeping the honest people honest" style protections.
