It is as simple as that: You don't wanna run any production system on an outdated software release. If you are reluctant to migrate to the new release of a software you will end up being unsupported and fighting bugs that have been fixed for a long time. Or even worse, you might hit a limit that has been lifted in a newer release and your database goes down and you can't fix it withouth a migration. If that happens, then you need to perform the migration at the time this happens to you and will take as long as it takes and your production system will be offline for that amount of time.
Just think about how much data growth there has been just over the last 5 years where the amount of data applications need to handle seemingly exploded. Plus, availability requirements, the service level agreement you need to fullfill with your application, have gone up dramatically.
The life-cycle of OpenEdge 10 is now more than 10 years ( the first OpenEdge 10 release was introduced 2002/2003 if I am correct ). Although it has evolved it is still a 10 year old software regarding concepts and architecture.
Plus you will miss a lot of improvements and features that you can use out-of-the-box just be migrating your database and re-compiling your application.
Heavy Regards, RealHeavyDude.