Buying a new house involves some of the most complicated and nerve-wracking tasks anyone could possibly undertake. In a short time, the typical buyer must seek out and qualify for a mortgage, find a lawyer to handle the closing, hire a moving firm, and engage a contractor to carry out renovations. There are utilities to be turned on, security systems to be installed, appliances to be bought. And you have to arrange for insurance. What buyer wouldn’t prefer to do business with a single vendor that could make or guide every choice and organize the countless details accompanying a change of residence?

Many retailers, building on their core merchandising and customer relations skills, may have the ability to pull all of these things together by offering a broad array of products and services to groups of customers defined by their common situation. In the case of a home purchase—or, for that matter, the entire span of products and services that homeowners want—the retailer might be the do-it-yourself superstore Home Depot, a chain already valued by customers for the home improvement advice its salespeople dispense. Further examples spring to mind. To meet everyday needs, Wal-Mart, the world’s largest retailer, could...