When I spoke to analysts and investors, they had all kinds of reasons for Amazon’s performance last year. “They finally reached a point where their R&D spending was not expanding as fast as their revenues,” said Citigroup’s Mark S. Mahaney. He and others also talked about Amazon’s success in international markets, its fast-growing (and high margin) merchant market, which allows merchants to sell goods alongside Amazon, and its rapidly expanding Web services business. Mostly, though, the investing community pointed to those healthier margins as the main reason for the stock’s run-up. Legg Mason’s legendary fund manager, Bill Miller, who has made a small fortune for his investors by betting big on Amazon, told me that “Wall Street is almost fanatically focused on margin expansion and contraction.”

But I couldn’t help wondering if maybe there wasn’t something else at play here, something Wall Street never seems to take very seriously. Maybe, just maybe, taking care of customers is something worth doing when you are trying to create a lasting company. Maybe, in fact, it’s the best way to build a real business  even if it comes at the expense of short-term results.

It is almost impossible to read or see an interview with Mr. Bezos in which he doesn’t, at some point, begin to wax on about what he likes to call “the customer experience.” Just a few months ago, for instance, he appeared on Charlie Rose’s talk show to tout Amazon’s new e-book device, the Kindle. Toward the end of the program, Mr. Rose asked the chief executive an open-ended question about how he spent his time, and Mr. Bezos responded with a soliloquy about his “obsession” with customers.

“They care about having the lowest prices, having vast selection, so they have choice, and getting the products to customers fast,” he said. “And the reason I’m so obsessed with these drivers of the customer experience is that I believe that the success we have had over the past 12 years has been driven exclusively by that customer experience. We are not great advertisers. So we start with customers, figure out what they want, and figure out how to get it to them.”

Anybody who has spent any time around Mr. Bezos knows that this is not just some line he throws out for public consumption. It has been the guiding principle behind Amazon since it began. “Jeff has been focused on the customer since Day 1,” said Suresh Kotha, a management professor at the University of Washington business school who has written several case studies about Amazon. Mr. Miller noted that Amazon has really had only one stated goal since it began: to be the most customer-centric company in the world.

In this, it has largely succeeded. Millions of people instinctively go to Amazon when they want to buy something online because they have come to trust the company in a way they trust few other online entities. Amazon’s technology, its interface, its one-click buying service  they are all incredibly easy to use. Its algorithms offer “suggestions” for further buying that actually appeal to its customers. Its Amazon Prime program  for a $79 annual fee you get two-day free shipping  is enormously popular. Unlike what happens at certain other technology companies, when you have a problem, the customer service telephone number isn’t hard to find. It is even willing to correct mistakes that it didn’t make, as I discovered over Christmas.

All of this, however, comes at a price. Indeed, as I’ve written before, customer service isn’t cheap. Certainly, a fair amount of the hundreds of millions of dollars Amazon has spent on R&D has gone toward developing, say, the Kindle, but a good deal of it has also gone toward improving the customer experience. Amazon is willing to lose money on some of its most popular items, like the latest Harry Potter novel. And even with Amazon Prime, it must surely swallow millions of dollars in shipping costs. Indeed, in a presentation to analysts in late November, the company’s chief financial officer, Thomas J. Szkutak, showed one slide that read, “Over $600 Million in Forgone Shipping Revenue.” And that was just for one year.