[dunham]

It's possible that only MobileSafari.app is signed with the entitlements needed to do JIT (write to executable memory segments?). The full-screen web apps open as separate applications and might not look like MobileSafari to the OS.

[comex]

Exactly-- only MobileSafari has the "dynamic-codesigning" entitlement, but full-screen web apps open in WebSheet.app. This is almost certainly an oversight. On the other hand, I doubt App Store apps will get that entitlement anytime soon.