I don't know, sometimes I believe that the cost is calculated by BTU's, using electric as a baseline.
That should be true, Residential Natural gas is often priced by the Therm. (1 therm=100,000 Btu, which is the heat content of about 100 cubic feet of gas)
using electric as a baseline
That part sounds doubtful. I do not understand how (or why) they would do that.
If you are interested, some more information may be found at:
Residential Natural Gas Prices
What Consumer Should Know
http://www.eia.doe.gov/neic/brochure/oil_gas/rngp/index.html
Release Date: November 2007
Next Release Date: November 2008
Judging from your home page, you probably already know this stuff, but maybe there is some new info there for you.