The author agreed that Sam's Club is the better comparison. But, since Walmart doesn't provide separate numbers, she was hamstrung in her efforts to do a more direct comparison.

However, it's rather strange that she didn't compare them head-to-head when such comparisons WERE possible. For example, she compares Costco's website to Walmart's. But Sam's Club has its own website and its incredibly busy home page has tons of expensive items from computers and digital SLRs, to swimming pools, all the way to the very same outdoor play "forts" Costco sells.