I've had the same doubt as these users with a question I had a year or so ago. It was a question about wording of a mathematical term. So, does that go to math.SE or to english.SE? All of your examples are the same: questions about engineering words, to such an extent that they were all posted to either english.SE or ell.SE.
I ended up asking my question on english.SE. However, I got the following comment on my question: "I expect you would get an answer quicker on math.stackexchange.com". I also got satisfactory answers on english.SE, but clearly my doubt was reasonable.
Cross-posting should certainly be discouraged, but it shouldn't be punished to the extent that both instances of the question get closed. Therefore, the question becomes which instance to close.
The comment on my question informs my opinion on the subject: I think I asked my question on the wrong site. Sure, it was a question that involved English, but which site would be most likely to give me a good, authoritative answer? Obviously math.SE. That's the site with the people that actually use the terms I'm looking for.
The same applies to these questions. Who is going to know where the term "bridge cam gauge" came from? A bunch of English professors who can tell you that "bridge" came from the proto-Germanic brugjo (hurrah for stereotypes!), or engineers who've used one (I haven't), who probably know why and how it was developed? I believe the latter (the professors are currently beating us in answering these questions, but I assume that's because they outnumber us 15:1).
So, to conclude: if either instance of the question should be closed, I believe it should be the instances not on this site. Even though the other sites are giving more answers to these questions, I believe we are the ones that can (eventually) give better, more authoritative answers.
That being said, if the question has been satisfactorily answered elsewhere, the instance here should be closed and a notice should point to the answer on the other site.