Remember that we're still talking about a life partner here, which is very different from, say, a roommate. As long as you and a roommate are respectful of each other's sleep, possessions, ability to host friends at least occasionally, and mutually agreed levels of general cleanliness, you'll probably get along just fine, even if you're different in almost every other way. You're two different people in different places in life with different goals and ideologies and you just happen to live with each other for now. It's perfunctory and emotionally cold, but that's OK, because that fits within both you and your roommate's expectations, given that the rent needs to be paid and you only have so much time to find someone to help you pay it.

Of course it's possible to be wonderful friends with your roommate, but the point to be made is that if that's your grand sum of what you expect out of a relationship, you're going to feel profoundly lonely, unsupported, and unloved. Fulfilling our emotional needs is also important, and dating sites that focus on finding people who are similar to each other are sites which understand that people will build that relationship of love, trust, and understanding on a foundation of what they have in common.

What the author is trying to remind us is that no matter who much in common we have with someone, and thus no matter who we marry, there will be areas in which we will differ from and disagree with our partners. As such, healthy dating requires you to find not only that base of similarity but also that ability to disagree without a sense of disappointment that you disagree with The One on something.

So the article isn't meant for people in healthy marriages. They already understand that. It's written for the serial daters who reject suitors for ultimately irrelevant reasons.