Existing architectures come embedded with their own policies with little control left to end user. It appealed to the enterprise customer as they only had to learn the knobs and how much to turn it before the product starts to smoke. This is about to change in Cloud Computing.
The forceful intermediation of an economic model into the use of an application (which the main difference between cloud and a cluster-grid) is disaggregating the policy definition point or PDP into multiple tiers. This is similar to what we saw happen to policy enforcement during the development of 3-tier datacenters in late 90s. A policy defined at the CSP level will be inherited, extended and enforced at the enterprise IT level and further changed and extended at the end user level. This requirement of the cloud will create a bias in the architecture of a system towards mechanism and policy negotiations.
The policy vs. mechanism was a hot debate in early 90s and looks likely to return once again.