@Mr Gumby: Yes, sure...
...until you start developing your ecommerce app on those servers, and integrating it with your CRM, and your helpdesk and marketing tools, and tracking clickthroughs and all the rest. These are ALL features that arrive out-of-the-box or as easily bolted-on apps with Salesforce.com, but require significant extra expense and effort when rolling your own solution.
Not to mention the maintenance hassle and expense. Okay, I understand that a lot of the readers here ARE maintenance expense, so they're not going to take kindly to the suggestion that that could be saved on, but there it is. I know a hell of a lot of people who WERE spending all their time and effort maintaining, who are now free to spend more of their time developing. They're happier for it.
Plus that "free" option they're offering is a hell of a good chance to try out developing a web app "in the cloud", and see how well it works for yourself, rather than whinging and backbiting. It's hard to see how an in-house solution could possibly come out cheaper than free; they even pay for the electricity and bandwidth. No outlay whatsoever to start developing, and you only start paying for it once you put it into production and start getting serious numbers of visitors? Sounds like a decent deal to me...
But then, I have drunk deep of their kool-aid, so it's not like my opinion counts, is it? I mean, It's only an informed judgement based on significant experience...
Anyway. Just thought the alternative view ought to be represented. Cue the indignant spluttering from the entrenched nay-sayers. Flame on...