Why reduced atoms are more energetic?
All electrochemistry is relative.  And any time you have a reduction or oxidation reaction, you are dealing with an electrochemistry problem.

NADH is "more energetic" than NAD+ because the hidden assumption is that energy levels are relative to reaction with the atmosphere.  NADH can react with oxygen in the atmosphere to release energy.  But on a planet with no oxygen and lots of hydrogen in the atmosphere, NAD+ would be the "more energetic" molecule.

Another less exotic example is anaerobic fermentation in yeast.  NADH builds up in glycolysis, and must be converted back to NAD+ through formation of ethanol + CO2.  That process consumes energy; thus, in anaerobic environments, often times NAD+ can be thought of as a higher-energy molecule than NADH.