Just the fact that a system can scale to a large number of nodes does not mean it is worth using.
Imagine a fictitious data system that scaled to 1 million nodes but could only process 100 bytes per second on each node.
This would be the worlds biggest energy wasting phenomenon, due to the electricity and cooling requirements for such a cluster. [arguably you could think of something else that wastes more energy than this :) ]
When supporters of a system start talking about how many nodes their system can scale to, don't forget to ask for an analysis of the efficiency of each of these nodes.
More later .... Ivan