My Grans bungalow
Exactly; sarcasm works here.
For regular cleans; such as domestic; a cold water system is fine. But if you have lots of large commercial stuff with infrequent cleaning schedules, then a hot-water system makes sense to get all that extra-grime off; quickly.
You don't have to use a sledgehammer to crack a walnut and the majority of customers, and let's face it for the average window cleaner, that's domestic work; don't require a £40K system to have their windows cleaned.
And I'm sure there's cheaper ways of getting a hot-water system than forking out all that for an Ionics system.
In fact I think Discount converted his cold-water system with some kit that cost him £300.