Wow, I'm glad I started this thread. I didn't expect that something so simple could be viewed so negatively, so that does give me something to think about.
I do want to say this, and not beat a dead horse. I'm also not married to the method. However, think about this: Sometimes steel wool is necessary to get a window clean. Sometimes a razor is necessary to get a window clean. Sometimes a magic eraser is necessary to get a window clean. Sometimes a scrub pad is necessary to get the window clean. But you will readily skip any of those methods if they are not necessary and you still get the window clean. So, sometimes (read usually) water is necessary to get a window clean. But if it's not, then why use it?
I was about to say that as long as the customer sees me wetting windows and squeegeeing, then I think there should be no issue with the windows that I'm dusting and essentially polishing. But, honestly, if I could do the outsides dry as well and the result was still perfectly clear windows, I just don't see how the customer could feel cheated. They are paying me to clean their windows. They are not paying me to mop and squeegee. If I mop and squeegee and the windows still aren't clean, I'm fired. If I dry mop and the windows are clean, they should be happy.
Either way, we are speculating on customer perception, and maybe you are right. Perhaps, customers just think mop and squeegee and need to see that to feel satisfied. Realistically, the only way to know is field-testing. Otherwise, we are all just guessing based on what we imagine a customer thinks. Taking my argument ad absurdum, you are also essentially saying that if I somehow invented a window cleaning laser that allowed me to clean the window perfectly just by pointing at it, that the customer would be unhappy with their perfectly clean windows because they didn't like how I got the result they are paying me for. By that same reasoning, I should be upset with my mechanic for using air tools rather than unscrewing every bolt by hand. I really don't care. Is the car fixed? Good. Did you do it in an hour instead of four? Even better. I got my car back quicker. Now let me get out of my customer's way quicker by not over-cleaning their windows.
See what happens when I get stuck at home doing accounting on a rainy day? I'm grumpy and have too much time to argue stuff on the forum.
Anyway, thanks everyone for all your feedback. I honestly do appreciate the counter-arguments because they've broadened my viewpoint on what I thought was a harmless idea.