A lot of the recent jailbreaks seem to depend on symlink shenanigans. I wonder why Apple can't simply remove symlink support from iOS' filesystem driver? Is there anything in iOS or the appstore apps that depend on it?
A few of those are created by the jailbreak but most are core parts of the system.
It doesn't seem like it'd be incredibly hard to remove those symlinks. Although Apple would probably favor fixing the bugs that allow malicious symlinks rather than remove symlinks from their file system driver (the horror!)
Plus, old binaries break all the time due to incompatible software or hardware changes (AVFoundation, GL shaders, UDID bans, etc.).
And new builds certainly get new requirements imposed (forced minimum SDK version etc)