As mentioned already, asking for your password is a security measure and as far as I am aware, there is no way, not even jb, to change this.
In your iTunes desktop version is a feature called 1-click which saves your Apple ID, but I think it only saves the password for music&movies, not for apps.
Pro tip:
Make a list of apps you want to purchase, then buy them all within 15 minutes, you will only have to enter your password the first time.