I've worked with people very used to working with enormously complex systems and even they say Walmart etc is on the higher end of that scale. We're talking weeks of people on site to get new software stood up.
This isn't to diminish your point about the need for upgrades, but it's nothing like a push button process.
Also, they should pay the vendors contracts for maintenance instead of trying to do the upgrades themselves. The vendors are generally more likely to do the testing necessary and have the skills for upgrading systems across from various customers.
At any rate, as you put it, eventually they still should do the upgrade.
If you want your POS to talk to your marketing automation system, that's another integration and maybe another vendor who Oracle may or may not wish to support etc.
There's no way for a bank to standardize on vendors as it's back office systems might have been designed in the 1980s. If it wants to add an iPhone app or mobile payments, it has to rely on another vendor almost automatically.
Making these stacks work generates huge revenues for people like CA, Automic, IBM. Process automation is big business. Big meaty huge Fortune 500 companies held together with the software equivalent of sticky tape.
Just to make what I'm saying more concrete: most people in my home town in Sicily think it's perfectly OK to bring their phones and laptops to some random guy owning a tech-assistance shop and tell him their Facebook/Email passwords straight away so he can reinstall stuff and save their login for them. Do you think they care about upgrading because of "improved security"? I'm not sure they even understand what a security issue is...
One can always hire experts with a proven track record to help with the install of the new OS.
Incidentally, many people may have trouble with upgrades to the new OS because 1. Running old hardware 2. Not running quality hardware -- e.g. for Windows laptops traditionally Thinkpads. 3. Do a fresh install. E.g. don't upgrade, but backup the data, clean the disk, do a fresh install.
I use Mac and did the fresh install of Sierra 10.12.1 and then upgrades for point version updates.
I also have been running Windows under Parallels and on Thinkpads prior to 2011 and not had problems with new versions of Windows.
http://www.dailytech.com/Appalling+Negligence+DecadeOld+Wind...
For example, Target and Home Depot were hacked because they failed to upgrade their point-of-sale hardware from Windows XP embedded to Windows 7 embedded or later which was an upgrade recommended by Microsoft. Windows XP embedded had a security flaw later patched in later versions of Windows.