Building such an elastic computing environment would need some serious computing power and, likely, a server room full of computers devoted to the task. With multiple computers, engineers would likely have the additional requirement that they want the system to function on multiple virtual machines that are allocated as needed so that the system is efficient.
Suddenly, a small project is getting big. Young, ambitious programmers would probably salivate at the prospect of creating such a system. But remember what I said earlier. What business are you in? This system they'd be building is not trivial and is certainly not something a lone programmer could throw together over a weekend.
That's why companies are intrigued by what Amazon offers: a massively parallel infrastructure that allows a customer's application to scale on demand, all without them having to worry about the nuts and bolts of making it work or the financial issues of maintaining their own data center.
In researching this article, I looked at much of the official documentation from Amazon, including one that describes the architecture. This article gives some great examples of how the EC2 architecture and other aspects of AWS can be a benefit; the one that caught my attention is an example of a system that needs to convert millions of pages of documents from one format, such as Microsoft Word, to another, such as PDF.
There are plenty of desktop applications that can do such conversions, and there are some that are available through a Web server, where a user can upload the document and transform it to PDF.
However, imagine hosting a Web site where users across the planet can upload their documents, and at times there could be tens of thousands of documents queued up. Such a job would be a nightmare. I would probably quit my job and move to another country the day such a system went live.
However, doing so in a cloud environment changes things. The massively parallel cloud environment could easily handle the system, and I probably wouldn't even need to have my cell phone turned on; I could actually sleep through the night.