That isn't the table you actually care about because it doesn't hit the residential customer like that. The nominal $/therm in my area has been stable for the last 10 years which might be artificial but to my bank account it's all the same.
Obviously depends where you are & your use, but most of the gas bills here are everything but the actual gas. Transportation, distribution, storage, taxes, standby charges...
What on earth is a standby charge on gas?
The monthly meter rental/connection fee/whatever your local utility calls it. Mine calls it "customer charge".
Natural gas prices have not remained stable in California.
I'm in southern California as well, and my gas bill in dollars per therm are not at historic lows. However, price per therm did not double this winter like it did last winter...so far.