First of all, there are two different questions here: serving tap water (hot or cold), and serving cold water.
Not serving tap water seems a reasonably clear case of gouging - or to be less judgmental, letting F&B places bulk up their margins on drinks...
Not serving cold water is something different, is definitely cultural, and it may be naive, but I've always assumed that water was served hot as proof that it had been recently boiled and was therefore clean and safe - obviously not such an issue nowadays, but if it's gone from a courtesy to guests to a tradition, that makes sense. Alternatively it could just be one of those strange (to outsiders, blah blah) Chinese food traditions which have very little meaning...