If you're on Lion, you can still download the 4.3 simulator (at least I did with the Gold Master version, presumably it still works with the final version).
In Mountain Lion, simulator 4.3 does not work (as can be seen from the first beta versions) and thus Apple was removed.
If you really need to, you can run Lion on top of Moutain Lion with Parallels Desktop or something similar that I do.
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