95% of things I just don't expose to the net; so I don't worry about them.
Most of what I do expose doesn't really have access to any sensitive info; at most an attacker could delete some replaceable media. Big whoop.
The only thing I expose that has the potential for massive damage is OpenVPN, and there's enough of a community and money invested in that protocol/project that I trust issues will be found and fixed promptly.
Overall I have very little available to attack, and a pretty low public presence. I don't really host any services for public use, so there's very little reason to even find my domain/ip, let alone attack it.
Potato, potato....
Whether we call them 'undocumented commands' or a 'backdoor', the affect is more or less the same; a series of high-level commands not listed within the specs, preventing systems engineers/designers from planning around vulnerabilities and their potential for malicious use.