Darryl,
You are correct that the DS2438Z can sense temperature. We offer a DS18S20 as an option because it is calibrated. In tests that I have done I have seen DS2438Z as far as 5 degrees off from a calibrated source, where as the DS18S20 have been about 1 degree off. Both the DS2438Z and the DS18S20 seem to track together it is just that every DS2438Z will have to be calibrated in the software where the DS18S20 comes factory calibrated.
Hope that answers your question.
Eric
