And you continue to ignore that a locked-down app store nonetheless offers more security benefits than one with a wide-open front door where the environment is equivalent (Compton).
Not true. There are numerous examples of locked down systems being broken because of the system being locked down.
One example is the GSM system. The encryption was fairly quickly broken because the designers had used a weak proprietary scheme. Had they taken a more public approach or used a public crypto system, chances are that they would have avoided this issue.
There is also a rather recent example of the iPhone security being completely circumvented.