Similar is not "exactly the same" so the people in question will have points where they disagree, but overall they tend to be similar. That's the successful relationship. We tend to seek out people who are like us, and bond with people who share our opinions or at least are in agreement on some things we deem important. Think about it--do you 'like' comments that go against what you feel?
Naruto and Sakura are similar in attitude, and they have some shared goals. They're also opposite in others, where she's more book smarts while he's more think on the fly. She's developed herself to becoming an exceptional medic while he's working to become hokage. However, they're both very proud and supportive of each other which I think is important. Also, what can happen in successful relationships is you begin to internalize your partner's goals, dreams and achievements as your own too. That sounds familiar to me. So on the points they're not similar, it's not causing as many conflicts.
NaruHina and SasuSaku... I dunno. They're opposite in attitude, though I guess Hinata is trying with some success to adopt Naruto's ninja way, but they don't have any shared goals or interests that I can think of? Sasuke and Sakura were exceptionally good students but those are in their academy years, and Sasuke is the opposite of supportive when it comes to Sakura so...
I dunno. I know in other manga sometimes "complete opposites" end up liking each other, such as the shy guy and the tsundere girl or something, but they usually find out that despite that they share a common value point. They're not usually bonding over their differences, but what they found they shared that's valued to them.