So, a screensaver that's mostly black can help save power, even if it doesn't actually use DPMS to power down the screen. Of course, one that's very bright and colourful, or that keeps the CPU running fast is not much help. Any program which can be invoked in such a way that it draws on the root window of the screen can now be used as a screensaver without modification. The programs that are being run as screensavers don't need to have any special knowledge about what it means to be a screensaver. They confirmed that the allowable stand-by power targets depend on the device, and they only knew their targets.
Timer based power savings are the exception.
Most savings come from designing in power on demand with low leakage drivers. For example, using stepper motors with low leakage current instead of high leakage. This savings is both from individual designs and from the resulting demand for low leakage products causing better and cheaper low leakage product designs. Energy Star was good organizational engineering. It never required designers to compromise quality or performance, which made it much harder to argue against design changes to reduce power consumption while idle.