Twtich, I'm referring to the idea that they buried the body with reverence and gifts inside the grave, not the practice of leaving flowers in rememberance. There is a practice in many palces and times of decorating the inside of tombs, or example.
But, to your point, we want to remember the dead because human life is special. If life is special, so is death, I'd argue. And, with death, suffering. In this way, a person's entire life could be considered a mystery, a sacrament, holy. The entire Christian approach is emphatically confirmed by the Incarnation, in which Being itself entered into humanity and experienced the totality of it: all the way to suffering and death.
If we think human life is special, then we are stuck with the observation that it will, on late night, come to an end and that the end is likely to include suffering. It isn't obvious to me that we should partition a life into those pieces that are special (good times with family, climbing a mountain, whatever) and those pieces that are not (the things associated with the end of it).
That said, I am in essential agreement with the original post, which compained about the simplistic and offensive approach of certain unspohisticated Christians. I am simply attempting to point out that these people are operating outside of the much larger Christian tradition. That tradition begins with the observation that Being itself assumes humanity and that humanity -- all of it, down to the suffering part -- is thereby mysterious, a sacrament. It is, as I have said, a point to begin thinking.
Otherwise, I feel that we are stuck with the idea that, well, cancer sucks and watching family members die sucks, too. And nothing more. Maybe it works for some folks, and that's fine. But the trend throughout human history has been to go in the other direction and, in a way, it is the very definition of being human. We shouldn't be too hasty in throwing that away.