Is Cloud a throwback to the mainframe era?

A common refrain that we hear is that cloud computing is nothing new but a fall back to the centralized model of computing that existed in the seventies. After all Virtualization is a technology whose origin goes back to the mainframe days and languished while the desktop took sway.
I do believe that people are missing the point about the cloud by comparing it to the mainframe era. Yes it does mean more centralization of resource pools but there are some fundamental differences.
Mainframe computing was about efficient utilization of scarce resources. Everything from CPU, RAM , storage and network were expensive and the goal of the mainframe operating systems and the system administrators was to ensure that these resources were utilized to the maximum and that there was no wastage. The decision to use 2 bits to store the year and not 4 was purely driven by the fact that storage was extremely expensive.
Cloud Computing is more about getting more out of abundant resources. The cost of computing resources (except network bandwidth) has become really trivial and are hardly factors in the decision making process.
Amazon's EC2 was really about generating revenue from idle resources and ensuring that their vast computing resources get better utilized. We can get terabytes of storage available at cheap rates but a service like dropbox offers convenience and an easy way to manage your storage needs across machines.
Cloud computing is about gaining efficiency in managing the computing resources. So while the cost of processing power and storage has fallen exponentially the limiting factor is in managing these resources.
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