What they're actually doing is conflating programmer and sysadmin here; the tasks they're assigning to the 'on-call programmer' are very similar to the ones I would expect as a sysadmin to get. Things like monitor the service, act as first responder, coordinate fixes; there's precious little that is actual programming there until you get into fixing it, and even there the goal is minimizing downtime, not debugging the change into working on the live system; typically "revert whatever changed" is one of the first tools for this work.
An actual need to do programming instantly and with no warning is quite a different proposition, not one that I'm aware of having ever been needed in any of the companies I've worked for.