Oh really? iOS has page-based executable code hash/signing since at least iOS 2 (2008); Android still doesn't have any runtime code integrity protections.
Of all the random security issues in the past 8 years you'd be hard pressed to find one where this was relevant.
At least someone is.
In a complex system great security takes years of work, it isn't flipped on like a light switch in v1.0. Wasn't the first version of iOS running as the root user?