Given the method by which the Americas were originally colonized, this isn't surprising if one thinks about it. The Arctic regions aren't very conducive to using bows and arrows nearly as much as spears. Bows and arrows are also pretty sophisticated technology that could only arrive from OUTSIDE North America if they didn't arrive with the original inhabitants over their migration routes.
Reading it is a bit of a "say what?" moment. But in thinking about it, it really isn't a mystery why this happened the way it did. The assumption was that everyone had them long, long ago. But we all know what assuming means.
I do love it when science proves the assumptions wrong, but it's immediately clear WHY they were wrong in the first place.