This is just a symptom of the fact developers are like cogs, where you drop them in and expect them to work with "legacy code" where as they guy who just moved

This is just a symptom of the fact developers are like cogs, where you drop them in and expect them to work with "legacy code" where as they guy who just moved on/was laid off had all that expertise on the logic and behavior that predates you. If you people decided to actually build with an eye towards longevity, (in this case, I mean keeping people around so they can train the newbies) then this wouldn't be a problem.