On large projects ( those with a code-base as large as a GB ) it's quite possible to lose existing API. This is typically due to insufficient documentation, or an inability of the programmer to locate the original code; hence duplicate code.
Boils down to laziness, or poor review practice.
EDIT:
One additional possibility is that there may have been additional code in those methods which was removed along the way.
Have you looked at the revision history on the file?
