@DZ-Jay
"Apple does not prohibit Web browsers on the App Store. It does require any HTML rendering to be done using its own API (which is the same Safari uses, being WebKit) and any JavaScript execution must also be done through its own API (again, provided by the WebKit framework, the same one used by Safari)."
Even assuming that's all true, it entirely misses the point.
Taking an existing browser, and then changing the "skin" to make it say "Firefox" is not the same as actually running firefox. Ignoring that, assuming the other browsers did just that, there is very little they can do to improve the browser now that it's running safari's back end.
Hypothetically, lets say safari fails some html5 test cases, and one would expect firefox or opera to work like they do on all other platforms, except they cannot because they're just shells around safari.
Another more serious example, firefox is likely to support ogg/theora on all platforms potentially offering a very significant benefit to end users. When it comes to the ipad version, they'll have to say the feature isn't supported since apple decided not to support it in safari.
Another example, firefox on the ipad would probably not be able to support standard plugins such as adblock, greasemonkey. This would be a major setback for the mozilla project on this platform.
In the end, users would blame mozilla for a shoddy/undifferentiated experience on the ipad, when in fact apple is the real culprit. Mozilla's decision was to have no browser on the ipad rather than one with apple pulling the string. Can you imagine how bad the situation would be if every device manufacturer acted the same way as apple?