mmicn
Your suggestion with regards to maintenance is indeed a valid one, but again the increase in cost is simply to big. Most financial institutions in my country and region (western europe) actually see ATM purely as a cost, and install them simply because they want customers to get a hold of their money. It is that simple. So why would they increase the costs?
I think, and I don't want to start any flamewars or anything, that reconsidering the use of Windows in its current form is a valid route. If you were to start from an extremely limited & stripped down version sure, but not in the way companies are currently using it (for those that might wonder, yes full installs of windows happen all the time).
Anyway, I'm glad this is in the open. The more people talk about it, the more things will change.