I think this is well-understood by all the players in this space. The problem with utility computing is that, well it's a utility. Ideally, the market becomes completely fungible, with the only differences being price and reliability.
There is a legitimate question about whether packaged software (e.g. Exchange) or SaaS (e.g. hosted Exchange) has higher margins, though. Getting customers to pay every month forever certainly sounds appealing.
It's easy enough to realise that you're always selling less (computing power) than you pay for. The margins are inevitably small, but there are other reasons to get in the business. For Amazon.com the main reason was probably to build such a huge economy of scale that they don't need to buy extra capacity in Q4.
