I carry a stove, but use it almost exclusively to make coffee. I cook on a fire because it's easy to control temp and means I carry less fuel. I don't carry a saw or an axe and rarely spend more then ten minutes gathering wood. The amount of BTU's in a one inch diameter stick of dry jack pine is amazing.

Nearly all my travel is in mid/late October and the warmth of a fire is welcome. When  tripping in summer I would go days between fires.  I would be less likely to use fire if I traveled in the BWCA, as IC points out the grates are often terrible for cook fires.

-The Beaver-  you are correct in that burning iso-butane creates less toxic emissions than wood, my guess is that the environmental impact would be greater if you considered the emissions generated by extracting the fuel and packing it into canisters.