Most of my customers dont bat an eyelid to which way it gets done, and most say, so longs as its clean i dont care.
The only people i do trad for is the oldies, i cant be bothered too, or explain to them how it works, as they just wont accept it (probably too set in their ways - however u may get some oldies that like and accept new technology). Most of them live in bungalows anyway, so im not bothered.
You will find that if you do it properly (wfp) it does give a better clean once dry, and it stays cleaner after it rains! (which i always tell my custies and i have seen the proof with my own windows), but many people dont want their cleaned windows left wet.
horses for courses as they say.