Tonya from Survivor Thailand's father died while she was out there - she did not find out until she was kicked off. Or possibly, he died after she was kicked off and she was not able to go home, I can't remember, but basically, the game interfered with her ability to respond as she would have normally.
But I can't believe that no one questioned Jon's statement that his grandmother was his first choice to be his visitor. Unless his grandmother is Rudy Boesch (from S1, heh), I find it highly unlikely that she would travel that far, especially with the possibility of having to eat something revolting, or having to stay in the camp with all the Survivors. It seems like he could have said his mother was supposed to come see him, and that she couldn't come because she was making funeral arrangements or something - whatever, no one even questioned it, which I find incredulous.
Actually, I'm fascinated by who Survivors choose to come visit them. Women ALWAYS have their husband or boyfriend (oops - ALMOST always. Jan actually had her son come), but quite a few guys have had their moms, or a sibling, or even a friend. I think that the choice of visitor can be very strategic. For some players, seeing their mate can reinvigorate them - but I think that a lot of them get incredibly emotional about it. If I were on the game, I would not have a family member come. I would want to maintain focus, and would rather have a friend show up. I would also choose someone that I think would have a chance at doing something physical or eating something gross.
guinevere