*sigh* No tombstone 
Well, I know he wasn't Jewish but in the Jewish tradition you don't put up a stone until a year after the burial, allowing the loved ones a full year of "firsts without" to mourn their loss and to commemorate the departed one's life. After a year, a stone is put up and an "unveiling" prayer ceremony is held at the site to dedicate the stone and to close the year of mourning.
In that sense, it's kind of nicely symbolic that there's no real gravestone up yet. I'd rather think of it in this context than that everyone is fighting over his estate or whatever. Come to think of it, we don't know if he had expressed any wishes about what he wanted, either.
So once again, who knows? Art seems to have left many mysteries behind, probably on purpose. <G>