Hot water cleans quicker on soiled, salted windows. Shrivels the spiders and their webs up immediately so less trying to scrub/flick their handywork with the brush. Hot water lifts the dirt much easier on new, stubborn dirt.
Give you an example: With an empty mug with coffee, tea stains at the bottom, pour a tiny amount of water in and swirl it around and see how easy the stain shifts. Then try it again with another stained mug using hot water instead of cold and you'll see for yourself why hot wfp users like hot water.
Also, with hot wfp the hose remains supple, doesn't kink easily, is a pleasure on the hands on cold mornings and easy to reel back in.
The hot water sheets down large panes of glass quicker and dries much quicker so on windy days when there is a lot of dust blowing around there is less chance of water left on windows collecting dust, salt, road grime from car exhausts,etc. Customers have less reason to moan about windows being cleaned and left wet.