Tamhas,
When you were selling ERP s/w what was the average size of your customer in terms of number of employees. I spent 30 years in IT at a large aerospace firm. Many of our applications had much longer lifespans than 5 years. When I retired (2010) we still had in house developed COBOL serial batch and IMS applications in production. Admittedly, these applications were specialized to the point that there were no COTS replacement and also certified by various regulatory bodies. Pulling them out of production would have been very costly (as a replacement would’ve had to have been coded in house), enormously disruptive and would have to have gone through a time consuming and costly certification.
But even those apps that could be replaced by COTS often had very long life spans. In the 70s I worked on an IMS replacement of a serial batch purchasing system originally developed in the 50s (which ran on an in house developed “database” and teleprocessing system). It was not replaced by COTS until the 90s. And that was not a smooth transition. I had been the lead analyst for QC receiving and transportation. The new COTS did not have a lot of the functionality that was in the in house application with respect to quality assurance requirements.
I think it’s safe to say, the larger the enterprise the more slowly new apps are swapped in for older ones. In the case of the purchasing system I mentioned, the driver for the first replacement was not functionality so much as it was a need to move to a newer technology base. The second replacement was a combination of drivers in that the new COTS purchasing system was part of a larger ERP package that replaced several in house systems. The move to the ERP s/w took years. The division president referred to the project as changing a flat tire while driving down the highway at 60 MPH. Production was at no time halted in order to make the transition to the new system.