I love car analogies. No, Ford does not prohibit you from installing a Chevy engine in your Mustang. They also do _NOTHING_ to enable you.
Actual technical limitations are fine. Artificially imposed legal/contractual limitations aren't.
More specifically: I don't expect Apple to provide a compiler for my favorite language (which is not Flash, I should add). If they only provide an Objective-C compiler I'm fine with that. On the other hand, if someone develops a compiler that can convert code from my favorite language into Objective-C, then I am not okay with Apple saying "you can't use that tool - you have to hand-write your code in Objective-C".
I don't know that I'd go as far as to say that what Apple is doing isn't within their rights, but that doesn't mean I have to like what they're doing. They're handicapping their developer base by limiting the tools they can use. Some developers will stay and put up with the handicaps, and others will leave. I have a hard time believing that that will work out for them in the end.