The inferno level requirement can be done in 2 ways - compulsory or optional:
In D2 ancient quest, it is a must to reach level 20, 40, 60 before passing through normal, nightmare and hell ancient, inferno act 1 - 4 can probably have the same compulsory restriction as before, maybe 60 - 63 for A1 then 64 - 67 for A2 and so on.
Player has to stay in same act a bit longer for getting used to how tough the monster will be in later act, other purposes are practicing with own skills, character abilities, farming better items or gold saving for later battles.
As this is a free country, optional way is to suggest a level requirement but player can still go to take some challenges with lower level. If player has excellent skills and nice items, they can enjoy faming in later acts (no drop rate discussion). If player dies very often, it is better to practice or farm in earlier act, otherwise high repairing cost is the penalty of underestimation, losing experience can be another penalty for unmatched level requirement.
There are gold and experience reward when completed most quests, I don't remember the exact gold reward amount for normal difficulty but 605 for hell seems pretty low, random dropped rare item can sell for 600 gold easily.
Also, item reward is not linear with difficulty. Charsi and Anya quest in D2 always gives rare item in hell difficulty, however a pure white helm dropped after completing a quest in act 2 hell which is not a reward, nobody is going to pick it up for less than 10 gold.
Player also has to do the quest for NPC (merchant) and reward is buying/ repairing item out of town, is that really a reward? It is not that hard for going back to town by pressing "T" button on keyboard. Perhaps, cutting down half of item price is much better as some magical and rare items are quite useful at low level stage.
Hope to see a better patch for D3 very soon.
Thanks for reading.