I know its a jokey thread but if the only thing hot water improves is the flexibiity of the hose then its money wasted, keeping the van frost free is not difficult or very expensive, (I use a £20 80W tubular heater from Ebay), I also find I get the days run done about an hour quicker in winter,due to windows been cleaner/lack of snail trails/bird poo/etc.added to the fact custies are less likely to want a chat, so I could see some may find that they are cleaning faster with hot but I am also cleaning faster with cold!!(in winter).
Surely the ability to start a couple of hours earlier on the few days when its sub zero,does not earn the £5K + running cost outlay.