offspeed vs standard speeds in iOS app (BlackMagic Camera)

Few questions related to “offspeed”:

1. It appears that Offspeed clips always lock a frame rate in the encoded clip. So...if locking is possible, then why isn't it also locked in non OS clips?
2. Why isnt 29.97/29.97 an option? (we can do 30/30 and 60/60, etc)
3. Is there any bit rate or other encoding differences between a standard clip and an OS clip or is it literally just a proper tag that is added to the clip that forces it to play at a locked rate?