The 'eth0' was hardcoded in the the powertop code.
The WOL status on interfaces named other than 'eth0' wasn't checked and for such interfaces the powertop doesn't show the suggestion about turning the WOL off to save the power.
The powertop-2.X handles the network interfaces different way. It gets the available interfaces from the sysfs. The problem was resolved by rebase to powertop-2.X
The new code handles the interfaces with arbitrary names correctly.