I think sometimes when people say 'I couldn't be in a relationship like that' they might mean right now - at a particular stage of life or marriage.
What you expect from your relationship depends a lot on your age & how long you've been together. Over the course of 10, 20, 30 years a marriage/partnership weathers a lot. Births, deaths, illnesses, conflicts, disappointments. You're less giddy with the joy of discovering each other, the sexual attraction loses urgency, having particular things in common becomes far less important than the fact that you've shared so much time and life. Hopefully you trust each other, respect each other, like each other and feel tenderness towards each other. But over time you both change, and the relationship changes. Sometimes you rely on each other more, and sometimes less - circumstances affect this as much as anything. I think we have a lot less control over the nature of the relationships we end up with than we think we do, and with any luck we manage to adapt and enjoy what we've got as it develops.
I also think people of a certain vintage are temperamentally / culturally less inclined to be earnest and effusive about their relationships. Those who've grown up with social media are in the habit of bubbling over with public praise for their loved ones; people of my generation, more accustomed to understatement, might be more likely to say 'we rub along nicely' / 'I don't want to hedge my bets' (or similar) to describe an incredibly devoted relationship.
At any rate, it seems lots of us are happy, so here's to us and our partners. 