My vote goes with the pilot. Until you cross the line you are still on the runway.
AerBabe: I landed once at Manchester (commercially) and the controller used "anticpated separation" when clearing a British Airways 737 for departure - assuming that by the time he had finished saying it, the Speedbird had read it back, opened the throttles and the aircraft had started to move at any speed, I would be clear.
All went well until my right brake seized on and the aircraft spun around again (ground loop style) back onto the runway.
Had I been on ground frequency by now, I would not have been able to stop the 737 - even worse if the pilot is inexperienced with a particular aerodrome, hasn't got the tower frequency memorised, and has tuned a single, old tumbler style King radio (no LED's with "flip flop" standby frequencies) to ground.
I will never tune to any other frequency until I've passed that line - it doesn't take much thinking to look up the taxiway before turning onto it - if there's something coming, I'll ask "Tower" - whilst also advising them that I'm, technically, still on the runway.
I do not know the wing span of the next aircraft to pass behind me - so I want to get off. As AOPA keeps trying to remind us here (USA) - the active runway at an airport is a very dangerous piece of real estate. Get off!!