I think you're right, Dan. My face to face group is currently playing a sandbox style Whitehack game (which is in the D&D family). As I was reading the first part of this, I wanted to disagree with you -- I was considering the object of our Whitehack game is to explore this setting and situation until we decide to do something else. But it seems like you focussed down on declaring the 'object of the game' == an ending condition. And I guess my object above does sort of include an ending criterion, but it's too soft to be meaningful. Our object is really have fun doing this for a while with no explicit end-goal and certainly none baked in to the game's rules.

That leads me to wonder if it's legit to claim the creation of the explicit end-goal is offloaded onto the group of players for pretty open-ended RPGs. But I think that a whole lot of games get started up with basically no explicit negotiation or discussion reagarding how the game is supposed to end.