Sounds to me like either they have just got their wording wrong, or that they are assuming hot water makes anything cleaner than cold.
In this case hot water will not benefit you at all. Stick to cold.
Probably the second, as in your example, I would personally ask for my carpets to be steam cleaned, as i have no experience in carpet cleaning and assume you steam clean. Now i know you don't. You see my point? (not sure if i explained it very well)
Learn something new every day