For most of the last decade, I looked at Amazon (AMZN +1.67%) and thought, "Amazing business, but too messy for me as a shareholder." I saw razor-thin retail margins, huge capital spending, and a company that seemed to reinvent itself every other year. Now I find myself changing my mind, not because the stock has gone up, but because the underlying business looks very different than the one I kept passing on. The profit engine I underestimatedFor years, I treated Amazon as just a retailer. Today, its own filings make it clear that the profit center is Amazon Web Services (AWS), not cardboard boxes.