http://daringfireball.net/2010/04/why_apple_changed_section_331

kreeger:

“And, obviously, such a meta-platform would be out of Apple’s control. Consider a world where some other company’s cross-platform toolkit proved wildly popular. Then Apple releases major new features to iPhone OS, and that other company’s toolkit is slow to adopt them. At that point, it’s the other company that controls when third-party apps can make use of these features.”

Makes sense to me. Objective-C and Cocoa Touch is what makes the iPhone what it is. If other developers write platforms on top of it that begin to lag or fail, and those become widely adopted, the software base also begins to fail.