I can't imagine that, either. I hypothesise that in Hell I'll smite Sarkoth quicker because I have high damage for a weaker monster, and the addition of Leah to make up The Trio (I only have Scoundrel in Inferno). After a few hours running Hell I should be able to compare the GPH to the Inferno run.
Edit:
I just did two runs by hand:
1. Hell for 5126 gold, and can one-shot Sarkoth. The cellar was open on my first game.
2. Inferno for 11,808 gold and was 6 shots for Sarkoth. It took four games to get an open cellar.
I think it will be interesting to see if the extra gold in Inferno makes up for the 6x amount of time it takes to kill Sarkoth.