That's a fair point, and it's your call - however, if the new (major) development is covered in this way then 1) users on the front page won't see mention of it at headline level and 2) the discussion of that development on HN will be affected by/limited to the time-decay of a post that is 12 hours older. I understand that there are tradeoffs at play, it really comes down to if the development at hand is big-enough to justify another post, and, again, that's your call.