Due to the very limited number of test conditions, we cannot draw robust conclusions about differences in power draw among browsers running Flash® and HTML5. We recommend conducting additional testing of a larger set of Flash® and HTML5 websites to draw more robust conclusions about how these technologies impact computer power draw.
It's good to start some energy efficiency ranking. Windows 8 (all tests are on that platform) have some very nice feature to helps developer on power consumption. My guesses is that no-one is using them as you need Win8 specific code but if somebody like microsoft try to MAYBE we could see some real differences.
Heuristics are bug ridden by definition. If they didn't have bugs, then they'd be algorithms.