Yeah, very cool. It only works because the rootfs is mounted as read-only or else they might end up messing it up if the system was writing to the same block. But then again if it wasn't read-only this wouldn't be a problem.
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)