They've given up on the little, pointless arguments about making the other one do something they have no interest in doing. Of course a relationship also consist of compromises and doing things for each other, as you say. Maybe this just isn't the best example. I am sure he does plenty of things for her he doesn't feel like doing. He said he'd think about coming along, but probably won't. She seems okay with that. I wouldn't find a relationship more healthy if he'd just agreed to tag along but still didn't really feel like it.
To stick to this example, why would couples have to do everything together anyway? She wants to see her mum, let her. He doesn't, so he can stay watch football. I think they handle it well. At least if she doesn't really hold a grudge and as long as there are instances where he does indeed go out of his way to please her.