I would assume it's because winter in Texas isn't necessarily cold, at all. For example, Houston has average hi/low of 66/47 F in February, as opposed to 94/75

I would assume it's because winter in Texas isn't necessarily cold, at all. For example, Houston has average hi/low of 66/47 F in February, as opposed to 94/75 in July. In the first case, you're running the heater sometimes, as opposed to the later case where you probably have AC on as much as humanly possible.