This is my experience, having worked in POS systems for a few years. The customers - especially huge ones like Walmart, Target, USPS - buy these systems on the order of once every 10-20 years for any given store. They don't want to upgrade them because they're expensive. Also, the companies that make the traditional ones were not very innovative when I worked there (20 years ago). Windows 98 had shipped and they were still using DOS on new systems.