In a 5$ wrench attack, it's more credible to say: "what passphrase? I didn't set a passphrase, see: my money's there, now stop hitting me!" instead of "I set only one passphrase, dude, I don't know what plausible deniability even is, and please stop hitting me now!".
XKCD is a helluva "meme generator".
But in reality the "5$ wrench attack" is usually more complicated than what the phrase suggests.
Armed robbers usually have some idea (right or wrong) about how much money you are worth. It can be as basic as "that guy must be loaded" based on your clothes and car; or a detailed profile of your worth and habits, from "casing" your home for several days, talking to talkative friends and service people, investigating your business, etc.
So, basically, robbers will not want your password in order to check how much is the balance on your Trezor. They will demand some satisfactory amount of money (or bitcoins, if they believe you have them), and expect you to do whatever you need to deliver it.
You may try to convince them that you have no way of providing the amount that they want, but that is risky: if they are forced to leave without the expected loot, they may kill you, out of anger, or to send a message to other future victims. If you have family, they will probably use them as hostages and threaten to kill them. On the other hand, "professional" robbers will rarely kill if they get what they expected. If you do have enough money to make them happy, you will find that it is better to give it up than to risk the alternative. Money can be recovered or earned again; your life, and that of your dear ones, cannot.
Robbers know that most people keep most of their dollars in the bank; so, normally, they will neither expect nor demand cash. (Although they may take you to an ATM and force you to withdraw as much as possible. And, if you
do keep lots of cash at home, they may well know about it.) But "bitcoin-enabled" robbers, if they know that you keep all your fortune in bitcoins, will probably assume that you can transfer all your coins from home, without contacting anyone else; so they will probably demand all that they think you own.
(I can speak with some authority on this: although I have never been robbed (knock wood), several of my friends and relatives have been, some more than once. And the student frat next to my home was robbed a couple of months ago. Robbers usually came gangs of three or more, often in daytime, with handguns or machine guns. Fortunately no one was harmed, and the robbers were content with carriable goods, such as laptops and TVs. They did not expect to find large amounts cash -- except once, when the gang had just watched the victim withdraw several thousand in cash at the bank. But they took any guns that the victims had at home, including the entire collection of one victim.)