For our power consumption tests, we measured the voltage drop across a 0.1-ohm resistor placed in line with the 5V and 12V lines connected to each drive. We were able to calculate the power draw from each voltage rail and add them together for the total power draw of the drive.
They used to put that snippet in every article (the way they copy and paste other things, like their explanation of using FRAPS on the methods page), but they apparently stopped doing so like two years ago. I'm not an electrical engineer, so I don't know how they're measuring the voltage drop or where in the circuit. If the quote doesn't answer your question, you should email it to Jordan Drake (jdrake at techreport dot com), the podcast guy, for the staff to answer.