It’s been called the “razor blade business model.” A company sells a product like a battery-operated razor blade handle at a relatively low price in order to sell a complementary consumable product later, like the astoundingly costly Gillette Power Fusion Proglide cartridge, $18 for four blades, which then get thrown away. But it could also be called the Keurig “K-Cup” business model. Once a consumer buys the coffee machine, the coffee drinker may spend as much as $50 to $60 per pound on the coffee contained in the K-Cups, considerably more than the cost of even Starbucks’s breakfast blend, which...