Physical objects (bridges, buildings, bicycles) require maintenance to keep them clean, working, and safe; periodically, worn and broken parts need to be replaced. Programs do not get dirty, wear out, or break; if ever a program is correct, it remains correct. In short, programs do not need maintenance. Yet there are two distinct activities that are commonly called program maintenance. The first is the one mentioned in the "typical software guarantee"; "maintenance" is used as a euphemism for "correction". This allows a programmer who is incapable of writing a correct program to declare success with an incorrect program, and leave the problem to someone else (for more money). This use of the term is just plain dishonest.
The other activity that is commonly called program maintenance is program modification to meet a change in specifications. After a program is in use, its users sometimes want it to do something different, usually something more, than originally planned. This is fair enough; users do not always know at first what they want or need. And it is fair enough to ask more money for more programming. But this activity should no more be called program maintenance than adding a new wing to a building should be called building maintenance. Reprogramming, as we may more properly call it, is not a separate subject; there is no special way to make changes and additions to a program that is different from programming in the first place. Of course, it will be easier if the original program is well-written and well-documented, and we should always keep that in mind.
If a bridge collapses due the incompetence of an engineer, the guilty engineer can be sued and jailed. Doctors, lawyers, and people of any profession affecting the well-being of people, are liable to malpractice charges if they fail to be properly educated in the their profession, or are presently many programmers whose poor efforts can aptly be described as malpractice. Improperly trained and using grotesque programming languages, they write programs upon which our lives and our fortunes frequently depend. For shame, we can and must do much better. There is no good excuse for continuing these present poor practices.