Death of hard drives...
For a benchmark aimed at testing servers and databases, TPC-C has increasingly been a test of major supplier's abilities to marshall huge farms of disk drives as TPC-C has a wholly untypical balance of server versus I/O resource usage. Until recently we have see (at the top end) vendors employing upwards of 10,000 enterprise disk drives. For this reason the storage hardware costs have tended to dwarf the server costs at the top end. That's very probably true of power consumption too - some of those storage configs must have been consuming close to a quarter of a megawatt.
The most remarkable thing about the current top-end TPC-C benchmark (from SUN) is that it included a vast amount of flash memory. Of the total database server and storage hardware costs (discounted) of about $10m two-thirds was down to the flash modules (about 80% was storage hardware in general). That was supplemented by a few hundred slow, 1TB driuves.
In contrast IBM's TPC-C (second on the list) had almost 11,000 15K drives - imagine the power consumption of that lot.
More attention to power per unit throughput is surely going mean that these mega-farms of spinning disks will be replaced in top-end TPC-C benchmarks with either full SSD or hybrid storage arrangements (as SUN have done). Reputedly the SUN configuration used less than 25% of the power of the IBM benchmark,