Janne in Osaka has a long and thoughtful comment on a previous post. I responded there to the technical and administrative points. I didn’t have anything useful to add to the broader issue that he raised: in short, How much do we want Big Brother to be our keeper? As Janne says, that’s a social and cultural issue.
Also, Anonymous kindly reminds me that 15 September used to be Respect for the Elderly Day (敬老の日), which the government celebrates by giving new centenarians gifts. In 2004, the national holiday was switched to the third Monday of September, but I suppose that it still makes some sense if only to retain the old date for making year to year comparisons.