Google Authenticator used by native apps?
Native Google apps don't use password (which you entered before activating 2-step authentication) everytime to log in. They only need it for the first time. After the first authentication, an Auth. Token is downloaded which is used for subsequent logins. As this Auth. Token isn't your main password, verification code isn't required at all. So, your apps continue to work without asking anything.

To invalidate this Auth. Token, you'll have to change your main password. Do it and you'll be asked to enter password in Android device. And, this time, your main password wouldn't work. You'll have to generate and use application-specific password. Native Google apps don't prompt for verification code. They only seek passwords which would let them authenticate.