Apple seem to use security primarily for two things, marketing, and to ensure they have control over the platform, and the developers who write applications for it.

Maybe that's three things? Anyway, the totality of what they do in security isn't user centric enough that the reason for external security hardware would be to primarily increase the user security. Obviously they have to do this (increase user security) to make it palatable to the customer, but there's a certain asymmetry in their actions that makes it seem unlikely that actual increased user security was the original goal.