Its more like this:
If the HNM you are hunting is a 70 hour respawn, SE changes it to a 15 hour respawn, HOWEVER, if you've killed once, you'll have to wait 70 hours to kill it again, otherwise it vanishes as an illusion. MEANWHILE, those who DIDN'T get a chance at the HNM who try to kill it, will be able to. So while it doesn't affect how the HNM remains a 70 hour respawn for the individual/alliance, it is respawning more often for others to get a chance.
The new coffer system means that the coffers respawn more often, but unless you are getting an AF piece or map, you are stuck on the old timer. So if it is just an illusion for you, that means that on the old system, there would be no coffer for you to pick because SOMEONE else already got it.
I think people are just complaining because the faster respawns are getting their hopes up. Aside from AF/Map hunters having more chances, the respawn for treasure HAS NOT CHANGED.