It's been known since the first iPhone security analysis, and it's what ultimately enables all these hacks on the phone.
My guess is that since Apple didn't intend on 3rd party apps to be running on the device immediately, they had some time to figure out the right environment for secure access to the phone's features.
And, to be honest, some of the threat is mitigated by the fact a phone is, by definition, a single user environment, and any software corruption that does occur can be resolved by a restore.
Also of note: part of the phone's filesystem that can be accessed when syncing is set to no-execute.
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