Diablo – Is Nephalem Valor supposed to work on non inferno difficulties

The entire Nephalem Valor concept has been removed since Patch 2.0.1 (live on Feb. 25, 2014). Along with this change, two new concepts have been added to the game (Official Patch Notes):

Pools of Reflection have been added to the game

• Pools of Reflection provide a 25% bonus to experience
• This bonus persists until you reach a set amount of bonus experience (equal to approximately 10% of the current amount of Paragon experience needed to reach the next Paragon level) or your character dies
• Gathering additional Pools of Reflection bonuses increases the amount of total experience bonus a character can receive until character death, stacking up to 10 times
• This experience bonus persists on logout

Nephalem Glory has been added to the game

• Occasionally during battle, monsters will drop Power Globes when damaged or killed
• Power Globes grant the Nephalem Glory buff, which causes players to deal additional damage in the form of golden lightning bolts and increases their movement speed for a short time
• This buff can stack up to three times

Difficulty is not (directly) tied to level, but rather Act completion. You can't go around in Nightmare mode until you've beaten all of Normal mode.

And what's more, you can go back at any time, so even if there are normal-mode specific achievements, you won't lock yourself out of them by rushing to Nightmare.