I like the rule "no feigning surprise". "No well-actually's" and "No back-seat driving" to me seem designed to help the linear flow of IRL interaction. But in a threaded discussion forum like HN, the important main thread can still go on unimpeded despite "no well-actually" side-notes.

The "no-subtleisms" rule is designed to hinder the spread of information about the differences of different groups. "It's so easy my grandmother could do it" is supposedly bad because it reminds us that there is a group, old people, who are not like us. Focusing on differences can create a hostile us-vs-them climate. But it can also remind us that there is a world outside of SV. That there are other people with other abilities and skills, with other problems that need solving. In this particular case it can remind us that if we want to target old people with a product, to make sure it is easy to use.