I agree that this could be a problem but in this paper in order for the attack method to work the developer of the App would need to explicitly set the keychain attribute with the flag "kSecAttrAccessibleAlways", making the keychain data available even when the device is locked, "Otherwise the credentials of the app are not affected by the attack method."
On iOS keychain access is not dependent on the passcode. Each application has access to its own keychain and cannot access the keychain for other applications. The keychain will still be encrypted even if there is no passcode set.
I am new and thanks, I now know what trolling means (I didn't mean it)! I posted this article because I believe it may put people off from developing with Objective C due to some misconceptions about the language i.e. no iOS Garbage Collection doesn't mean that Apple are two generations behind Java or .NET or because only 6.1% of developers use Objective C means its an awful language to use.