Emerald Oracle said:
Probably? I think (with all my voluble knowledge of Japanese Culture) that it's the demure young lady thing. Plus, she's much closer to the Japanese ideal of physical beauty than any of the other female characters... I think? The dark hair + porcelain-like skin y'know. Same reason the Sauce is more popular over there, he plays into a lot of cultural stuff we occidentals just don't get, or at least don't get on as visceral a level.
However, I think there's something else at play in regards to the characters. Possibly the reason why Sakura never took off is because of her strong attachment to Sasuke and her dickish behavior towards Naruto turned many off to her right away. Totally different from a tsundere, since she doesn't give Naruto the d(ere), and Sasuke mostly doesn't feel her t(sun).*
*Yes, there's an awkwardly placed joke about Sakura giving Sasuke the D, while Naruto is constantly feeling her T. Moving along...
Hinata, on the other hand, strongly supported Naruto to point that she tries to help him out in the Chunin Exams, despite the cutthroat nature of the tests (as well as possibly risking her own team's DQ). Also, remember when Naruto swore on Hinata's very blood to beat Neji's ass six ways from Sunday? When I first read that, I was like, "Damn, that's some romantic shit right there!" Because holy shit, you would have to really like someone to be that damn hardcore, and swear upon their life essence to do something. I know if it was me, I'd seriously have to have something towards that girl to be like that, man. I don't go around swearing on random girl's blood for no reason.
And, let's face it, her desire to be stronger, get better, even if she's a failure, too, has all that adorable vibes on it. Makes you want to protect her, y'know?