I don't really believe that. American public schools have been teaching the metric system to middle schoolers for a few decades now. Every American I talk to understands the metric system. In some cases, particularly units of volume, they understand the metric system better than the imperial units (liters are easy, but I can never keep quarts/pints/cups/floz/etc straight in my head.) Coca Cola sells sugar water to Americans in liter-oriented packaging (.5, 1, an 2 liter bottles are ubiquitous), and Americans certainly don't balk at that. They drink it up.
Also, 24H time system is something people often don't get, and only know about it as "military time", due to army actually using it.
Anyway, my point in all of this is that if a pop-sci publication like Wired uses units like kilometers, it is unlikely that their American readers will be confused. They'll probably walk away from such an article with a casual understanding of the subject that is reasonably close to the casual understanding they'd have if the article used miles instead.
Speed was easy, relatively. Even weight/height was alright, though Aussies tended to use imperial for those often anyway, including the whole 'stone' thing that threw me off at first.
Pardon me, the ignorant American... but this is who I am :D