I just had a death a few hours ago, and I noticed that too. Everyone was asleep, but they all woke up to go see him die. One thing to note is that it wasn't all the sims in the household- in fact, it was his wife and daughter that didn't wake up to see him. I think this was because of distance- all the sims who went to see him were in bedrooms right next to where he died, while the others were further away. And when another sim died off lot a while later, nobody in the house went to see him. I've got two elders whose age bars have been bubbling for a few days in house right now- I'll see how the other sims react to their death.