Why do I need to buy a World Travel Adapter kit at all? Won't the adapters that come with the Apple device be sufficient with the appropriate plug?

We're going to New Zealand and trying to figure out what we need to charge our iPhone 5 and 3rd generation iPad when we're there. The adapters that came with both devices cover 100-240V - 50/60 Hz.

Apple World Travel Adapter Kit

Apple World Travel Adapter Kit

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