Technically, this looks like a cool hack.

I've never found submitting an app for app review to be that big of a deal, if your app is well designed, useful, and not negligent or malicious toward user needs.

Your FAQ says what you're doing is explicitly permitted by Apple, and points to section 3.3.2 of the iOS Developer Program Information document.

But what about section 3.3.3?

    3.3.3
    Without Apple’s prior written approval or as permitted  
    under Section 3.3.25 (In App Purchase API), an
    Application may not provide, unlock or enable 
    additional features  or functionality through
    distribution mechanisms other than the App Store
    or VPP/B2B  Program Site

Finally, you do realize that the App store policies are subject to change in order to adapt to hacks like this, right?

Again cool hack but it will be interesting to see if it gets out of the starting gate.