It is what they THINK the birds need. I'll bet none of them stopped to really think about it.
I'm going into my 5th winter with chickens. My birds have experienced an all time low of -23F and lots and lots of nights with sub-zero temps. I don't heat my coop. I DO provide ample amounts of...
There are no conditions under which a fully feathered chicken would require any supplemental heat in your climate.
As @Ted Brown has already pointed out, ventilation that does not allow drafts across roosted birds is absolutely the most important thing to keep your birds dry and comfortable...