Shyness in anime and Japanese culture

So there's a girl who blushes at everything, feels self conscious about her uniform, has a crush on someone but is too afraid to talk, and when she hears a joke, she has a slightly embarassed look of flustered chagrin as her eyes squint and her cheeks raise, symbolized as ^^.  And she has a sweat drop on the back of her head.

Why?  In an age where modesty means nothing, why be shy at all?  A look at US voice actors in anime dubs will often have girls trying their hardest to imitate or act shy like their character, only to come off as overexaggerated.  And in the US, there's probably a lot less to be shy about.  Girls talk just like guys, know the same things, and can be just as outgoing.

lets put this another way. In the US, your average wild party will see girls dancing wildly and flashing their boobs while drunk.

In Japan/Asia your average wild party would just have a load of drunkeness with no girls stripping off unless they were hookers.

Thats the difference.