If I were in Apple's shoes, I would have taken another tack...
'Your iPhone is currently in Apple-only mode. To allow installation of apps not reviewed by Apple, you must disable this mode. Doing so requires a device reset and some apps may only function in Apple only mode'.
It's an interesting idea, but that ends up being a tech support nightmare for Apple. Some website or random friend says "Download this App - you just have to switch into non-Apple mode" and your non-tech-savvy friend doesn't have the experience to consider this suspect. Apple has to deal with that rather than the website or the friend.
