The real reason is this:

https://github.com/jashkenas/backbone/pull/3003#issuecomment-37276641

and this

https://github.com/jashkenas/backbone/pull/3003#issuecomment-37379087


You MUST have a compliment `undelegate` for pretty much everyone else. The only way to guarantee all the possible `undelegate` implementations will be somewhat compatible is to put one here and have the tests specific its behavior.