Actually, there is a lock screen in landscape mode. It is just not used for some reason.
To see it briefly, you can start the camera without unlocking the phone (from the lock screen or with the hardware button). Then, touch the small image of existing picture to go to the gallery mode. Now, the phone is locked and will display the lock screen before going to the image gallery. Since it is on the landscape mode, you will briefly see the lock screen and can even manage to type a digit or two if you are fast enough. Unfortunately, then it changes to the usual portrait mode no matter what.
So they actually implemented the screen but are not using it. Can't see the logic of that, really.