I think the difference is that RTH physically moves the craft to the home location, while home lock requires the pilot to manually adjust pitch to move it. I suppose, too, that if the home lock feature were working you could fly the Inspire out somewhere and manually set its location as the home point... then use home lock to move there from some other point, while you controlled pitch and the camera. I think home lock is more about orientation and maybe camera work than a failsafe.
Personally, I'm not all that interested in home lock... it's the POI mode in IOC that I want. That's one that I definitely think would come in handy for shooting. Set a POI, then keep the Inspire pointed at it. Yes, please. I really do hope they're actively working on finishing IOC.