"Apple's approval process ensures at least a basic adherence to expected UI behaviors and acts as an effective filter for malicious software."
It's not a very effective filter, since several apps on the store have been taken down because they violated ToS and nobody at Apple caught it until users did.
You're right, it's much easier to detect TOS violations and yet they are still failing to do so. If the description of an app is in clear violation and it still gets posted, what are the odds that they will catch an app that sends the developer everyone's contact list?
It's not a very effective filter, since several apps on the store have been taken down because they violated ToS and nobody at Apple caught it until users did.