The comments on that article are hilarious.
They assume an aluminum body would prevent user-replaceable battery, which we do not know.
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My (limited) observation of iPhone 5, suggest aluminum is too soft and insufficiently scratch resistant.
My older iphone 4 & 4S have a brushed stainless band around the edge, and even those show wear!
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But plastic or metal, I'm still a proponent of some sort of case.
edit: ...or bumper. And a screen protector (often a 1$ item).
Light duty or heavy duty, as befitting your use and clumsiness.
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