As far as I remember Tim didn't mean to have it in the first place while he was writing it, but he probably let it slip as we needed to finish the release... and other things.
As we talked earlier on IRC:
So, as long as this won't cause any performance issues and extra copies... lets remove it. you could create a JIRA and deal with this later. (Add a TODO on the code so we know about it when reading the code).
IIRC this method is necessary since at some point we have to get a reference to the underlying Netty buffer before the buffer is sent to Netty. If you didn't have this you would have to do an ugly cast.