There is a different level of criticality for "my post didn't go through, hit refresh" and "my transaction didn't go through - the restaurant said my card isn't working."
Would you honestly want to go to a bank and say "if we unplug this, we can find out what fails."
Facebook handles money too, though. Also I think the parent was making the point that Facebook builds software with resiliency in mind so when a failure does happen, the software deals with it gracefully.
They can have (and did have, at least the long time ago when I still used it) weird cache persistency errors and "please just refresh to fix that" type of workflows if you have bad luck. That sort of behaviour is simply not acceptable for a bank.
Would you honestly want to go to a bank and say "if we unplug this, we can find out what fails."