IPhone :: Restrict Access To Messaging And Mail?

i don't understand why it is not possible to restrict access to messages and mail, this feature is important in different cases like:

you give you child a phone and don't want to text all day with their friends, also if your kid is less than 13 years you could block this feature so that he can't chat with strangers.

also this feature is important because if you enable this feature you could have 2 different passwords for accesing messages or mail, this is important when your friends or family knows your main password but they don't know they password for restricted apps.

why would some one wants to block Internet, camera, safari, and other apps but you can't block messages or mail?

info:
imac, mac os x (10.7)