Why are preinstalled apps not registered in play store on new devices?
It's because Google can back up which apps you have installed on your Google account, and restore them when you associate your account with a new device. Since your friend's account is new, the apps have not been installed yet, and are therefore not shown.

As for why the apps are not shown as installed, it's because they're not installed from Google play, but from Samsung. If I remember correctly, Samsung has it's own Samsung Apps app, which handles updates for preinstalled applications unless they're associated with their Google Play counterparts.