It's not necessary but I saw big companies with different budgets for development, (manual) testing, maintenance, operations. The team for testing is definitely separated from the development one, different managers, goals, etc. Operations more like so. Maintenance and bug fixing could be done by the same people but there is always tension at management level about whether to prioritize new features or fix problems. There are different internal customers behind those requests and turf wars are fought every now and then. Different teams and different budgets solve part of that problem but of course the fixes of some bugs can become new features on their own and more turf wars follow.