There has always been a screen orientation lock... in one place or another. iOS 4.3 will give the users the option of using the switch under the volume control as a mute button (as it is now) or going back to the screen orientation lock.
Just remember this is only a beta feature so far. I can't think of any reason Apple would remove it from the public update, but we thought we were going to get all the AirPrint features last update too.