How many of you can honestly say you are 100% happy with pure water? It drives me stupid not getting perfect results, spending around £10,000 inc van on a system that gives less than perfect results. This invention is still not good enough in my opinion. It doesn't matter how long i scrub, how much i rinse, how clean my water is, I want perfection. No grubby corners, no runs of spots, no odd spots in the middle of nowhere just lovely clean glass that i cant pick fault with. 
Maybe you should have spent 20 grand instead of 10 to get better results
Seriously though, although I'm reasonably happy with most of the work I do, there are a number of jobs that could be better. I've tried all the recommended ways to change things. I still feel that most jobs, most of the time, are as good a finish as trad but I wonder if that's good enough. I take your point about spots sometimes appearing but my main concern is that fly poo (if that is what it is) doesn't seem to shift so well. Not such a prob on ground floor as it's easier to see and a quick thumb nail solves it, but on an upper floor, it could just be stuck there, unseen from the ground.
I suppose that in the interests of safety, a customer must accept that there may be times when a job is not totally perfect. In any case, if you view a trad cleaned window from inside you will sometimes see imperfections too.