This comment extends further into the realm of speculation than the original post. The article doesn't even mention Apple's understanding of encryption, let alone specifics like algorithms and key sizes.

The post only speculates about the meaning of Apple's carefully worded feature description, the scope of the device encryption, and whether it's primary intent is to enable the remote wipe feature.

With regard to four digit pins - the strength and length of a password is hardly immaterial to security if it is being used to derive or encrypt the key. This is especially true if the wipe needs to be triggered remotely. Storage of the key on the network or MobileMe would present a host of other issues that I suspect Apple would want to stay away from.