Keep in mind that they're talking about hardware control systems and not compute nodes. On these machines, the savings would probably not be too big (no/few consolidation gains). It also sounds like the decision was less about the upgrade cost and more about avoiding failure risks.

I also ran the numbers for fun. They estimated the cost to be 5.4MCHF for 2200 machines. Assuming 0.2CHF/kWh, they would need to save 140W per machine for 10 years to offset the upgrade cost. So, yes, it could indeed offset a good part of the upgrade cost over time.