The code-with-accompanied-documentation is somewhat a sub-case of a more general fallacy: the belief that a company can simultaneously maintain two different code-bases (say two code-bases implementing the same functionality in two different languages), while keeping them both synchronised.

The Extreme Programming experts have been warning against it, and it also makes sense that it is hard to do given that programmers, by nature, lack the appropriate discipline to keep maintaining two or more code-bases at once.

One possible solution to this problem has been illustrated by Fog Creek software. What they did was implement a compiler from a common language, to several target languages. Naturally, this compiler also needs to be maintained and extended, but it is less work and less error-prone than maintaining several different code-bases.