They're not always? You have to be a certain personality in order for that combination to work. If the wife wants to be the dominant one and the husband is more comfortable taking direction from his wife than making his own decisions then by all means this could work. However if you have two dominant personalities there's going to be nothing but constant bickering, two submissive personalities and they'll likely lack direction and succeed at accomplishing very little. In my own relationship my boyfriend has his life and I have mine - when we come together it's a 50/50 blend of ideas, goals, and directions. We work together and come up with solutions neither one of us could come up with on our own. I couldn't imagine anything better.