Many More than Two
You write, "The cloud is still relatively virgin territory with effectively two vendors - Amazon and Google - setting the pace and defining the way people think about it." This ignores the Force.com platform as a service (PaaS) of salesforce.com, which provides on-demand access to hundreds of applications from several hundred partner companies -- in addition to the applications built and offered by salesforce.com itself.
You also write, "deployment is defined by two approaches: virtual machine images like Amazon EC2 (known as Amazon Machine Images or AMI), and direct code deployment..." -- but Force.com defines a third model, giving developers the rapid time to market that's provided by a high-leverage API running in an environment that treats all customizations as platform metadata. This allows those customizations (data, workflows, custom logic, and user interface) to move forward transparently when the platform itself is improved. It's a difference that makes a difference: the CEO of ERP vendor CODA plc has estimated that his company saved "at least two years in elapsed time and at least 25 man-years of development time" by building its latest offering as a Force.com application.
Biting the hand that feeds IT
