I'm not saying every bit of dialogue has to be important for the story but there needs to be a reason it is there.
That's an important point.
By itself, the scene you quoted add a bit of realism to the story, because yes when we goes to a restaurant this scene happen. But is this "bit of realism" really needed ? It's debatable.
Every time one write a piece of dialog, he should ask himself "what did it add to the story ?" And if he don't find an answer, or if this answer limits to "realism", then this piece of dialog is totally useless and should be removed.
This doesn't mean that every player will find this part interesting or even useful, because everyone will have his own reading, but as the writer you should know why every dialog is in the story.
Of course, there's the "bit of realism", and it matters.
Passing from, let's say a discussion in the car, to both seated in the restaurant and facing their meal, would be bad. But there's so many way to do this while still carrying a bit of information in top of the bit of realism.
To stay with your example, "I'll take the steak, as usual", or "heard their steak are good, I'll take one", already change a bit the feeling, because the player will feel like he learned something ; the husband is a man of habit, or they never came in this restaurant before.
By itself the relevance of the information isn't the most important part, what matters is that this information exist. We know a bit more about the husband, therefore he's a bit less of a stranger. It's because of this that, when closing a book for the last time, we have this "goodbye my friends" feeling. The characters were total strangers when we started to read, but aren't anymore when we stop. It's never just the story that we miss, it's the company of the persons with who we traveled through this journey.
