It's not the license cost that's keeping these people from upgrading. It's verifying that the hundreds of applications, many of which were built by systems integrators that you have a strained relationship with that need to work correctly on whatever you're replacing it with. It's training users - some people "need" a two-day offsite seminar and a couple of weeks of reduced workload to transition to a new system. Also, something invariably goes wrong, so you also have to account for lost productivity when that happens.