I don't consider the 3.3.1 situation to be relevant, as in this case you would be running the official Apple toolchain.
If you had brought up the section of the iOS Developer License Agreement relating to "non-Apple-branded hardware" you might be in the right ballpark, but the legality of a similar clause in the Mac OS EULA was cast into doubt in the Psystar case. Psystar aside, the (non-commercial) OSx86 scene continues to thrive, unhindered by Apple.
At the end of the day, given that you would be running the official Apple toolchain, how would Apple be able to prove that a particular iOS app was not built on a Mac?
However, GCC and friends are licensed under the GPL: the code is published at http://opensource.apple.com; their only technical barrier so far is actually making it run on another OS.
That's not to say they couldn't block something like that, but with GPL code it does become significantly more difficult, if not (technically, not "this would take forever to port back to Linux") impossible.
I agree that this is a fair piece of precedent, but I would also like to note Apple eventually removed this clause and developers are again free to develop in other languages.
