I think it's due to thoughts that one is out of her league therefore no action is necessary. I undertsand it makes it more challenging to ask girls like that out, it shouldn't be though. So long as you eliminate from your head the reason for doing so. You can always approach and hang around with anyone for no reason, that's how you should do it with gorgeous women as well. They're just people.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~