I asked Dean Stewart, Senior Director, Self-Service Product Management at Diebold, Inc, why all the talk is of Windows 7.
The answer generally lies not with the ATM, but with the ecosystem the ATM sits in. Bankers are conservative by nature. They have invested a lot of time, effort, and money in creating a secure maintainable environment based on Windows 7. The environment is not just the ATM, but the teller platforms, thousands of PCs, servers, and other systems.
They want to maximize their return on that investment. They will run Win 7 until the end of its extended support in 2020. Only a very few have expressed any interest in Windows 8.