My view is that you probably won't see the HP/IBM/... companies enter this market as it's already commoditised (even though there's only really one player): they prefer to focus on high value, high margin products and services.
Sun is the only one in the space: http://www.sun.com/service/sungrid/index.jsp - they're currently task-centric grid computing rather than machine-centric cloud computing.
In many ways, running applications on a grid rather than machines in a cloud is a more pleasing idea, and fits better with the point I make in the post, but pragmatism wins out: the edge cases and dynamic requirements mean running virtual machines is often much more convenient.