I seem to remember that those classes were initially removed and then re-added by Josiah for backward compatibility (see discussions in issue 1641 and issue 1736190).

Despite practically useless after the changes applied to asynchat in Python 2.6, both classes are there since the very first checkin of asynchat.py, and the common policy in this case is to grant compatibility with older code, just in case few person out of many still rely on it.

I'd be more for stopping to mention them in the documentation, also because now that I look at it, the doc is wrong as it claims that "Each channel maintains a fifo" while this is no longer true since fifo() has been replaced by a deque().