Air temp is used in operations many ways. Too hot, speed is reduced in case of sun kinks (ooops, now supposed to call them "thermal misalignments" I guess someone complained). Too cold, many railroads also reduce speed for a variety of reasons depending on how cold, but some of the reasons include, rail pull aparts, rail/wheel crystalization issues (extreem cold), air repeater car requirments (or have to reduce train length) and more. If you run a print out, the temps given are degrees above ambiant temperature of each wheel bearing.
Nearly all detectors measure more than they broadcast over the radio. For one, Train speed is always noted even if it is not broadcast. Trivia, the rail temperature is almost always different than air temperature. For example, depending on the angle of the sun, on a hot sunny day, the rail can be more than twice as hot as the air temperature. This has to be factored in when the rail is installed, particularly when installed on concrete ties.
Rail head temperature also rises when the train rolls over it, particularly the heavy cars.