I agree with your point that all flights should be on airworthy planes. The OP's point seems to be: "My flight should have been airworthy when scheduled. It wasn't. As a result, I missed my connection, which US didn't even bother to hold even though I (and other passengers) was delayed because of a mechanical problem for which US is responsible."

Ideally, all flights should be airworthy at the time of travel. I'd imagine that at least 95% are. The others get delayed. If my flight is delayed an hour or three because of a mechanical problem, I'd still take it in stride if I have no connection. But if a mechanical problem ultimately causes a passenger to miss an entire day at his destination, some form of compensation is warranted. Perhaps a domestic F upgrade when available; that would be a nice gesture that costs US little while letting the passenger know that US takes responsibility for this passenger's delay.

But when customers hear employees say "You got there safe. That's what matters", it makes it hard for us to believe that US is willing to take responsibility for not having its planes ready to go on time.