If I were a bank owner, I would most certainly consider using embeded versions of Free Software operatings systems, such as GNU/Linux. That way, you don't need Microsoft to continue to support the system... instead, you could get any group of devs could be hired to do the writing.
I don'k know about that... I don't know about other banks, but at Wells Fargo, I can view my statement directly from the ATM (and items I bough via credit card just moments ago). I can also tell the machine to send a copy of my statement to my email. Therefore, I'm willing to bet that security will be a very hight priority for these machines.