Amazon's cash cow isn't quite as competitive now as it's been, raising red flags of its future profitability. Any investor keeping tabs on e-commerce giant Amazon (AMZN 0.80%) probably already knows how important its cloud computing arm is to the company's bottom line. For those who don't, the bulk of its revenue still comes from selling merchandise to online shoppers, 58% of last year's operating profits came from Amazon Web Services, even though this business only made up 17% of Amazon's total sales. That ...