The aspect of cloud computing that vendors appear to have decided will be the main attraction for business is flexibility.

At VMware’s European expo last month, the virtualisation company’s recently-appointed COO Tod Nielsen gave me the one line pitch for cloud computing that he gives CIOs: “Prior to the cloud, businesses had to provision computing resources for their maximum capacity, but the cloud allows you to provision for your minimum capacity.”

Amazon.com, the online bookseller and pioneer of cloud computing, today announced an addition to its Amazon Web Services cloud tool kit that will add to the benefits of utility pricing, namely ‘reserved instances’.

This service allows businesses that know when their peak requirement will fall to reserve excess capacity that they don’t need day to day. By giving Amazon advance warning of fluctuations in demand, this allows the company to provide those resources at a discounted rate.

“You make a low one-time payment for each instance you want to reserve and in turn you receive a significant discount on the hourly charges for that instance,” writes Amazon.com CTO Werner Vogels in a blog post on the topic. “Furthermore, you don’t pay hourly charges at all during periods when you have the instance turned off.”

In theory, at least, ‘reserved instances’ look like they will allow businesses to bootstrap their IT resources to their requirement even more tightly.

But it also points to a more sophisticated market for commodity computing resources, with a variety of pricing offerings that can precisely meet the financial and computing requirements of a given business.

This was the predicted outcome of utility computing when that model was first mooted years ago. And it is this, not any technological development, that at the moment appears to be cloud’s biggest selling point.