Amazon bought Whole Foods last year for $13.7 billion. One of the company's first moves was to provide a heap of discounts to Prime members who shop there and offer curbside pickup for online grocery orders. Grocery delivery services weren't far behind. The move sent shockwaves through the industry, with everyone from independent grocers to Walmart wondering what's coming next. But Walmart is not some local mom-and-pop shop to be muscled out or pushed around. No matter how big Amazon gets, Walmart has a powerful weapon that Amazon does not — 4,672 U.S. stores. In fact, 90 percent of America lives within 10 miles of a Walmart and its huge array of products. With groceries accounting for more than half of Walmart's business, that's a street corner worth defending — and defending it, Walmart is.