If that were to happen, theres no lock-in advantage. If, say, a mobile Flash software platform which encompassed multiple lower-level platforms, running on iPhone, Android, Windows Phone 7, and BlackBerry were established, that app market would not give people a reason to prefer the iPhone.
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And, obviously, such a meta-platform would be out of Apples control. Consider a world where some other companys cross-platform toolkit proved wildly popular. Then Apple releases major new features to iPhone OS, and that other companys toolkit is slow to adopt them. At that point, its the other company that controls when third-party apps can make use of these features.
Gruber also believes that these cross platform compilers rarely produce high quality native apps. Steve Jobs reiterated this point in a followup email:
Weve been there before, and intermediate layers between the platform and the developer ultimately produces sub-standard apps and hinders the progress of the platform.
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