The only grenade being rightfully declared dead is the Krak. Kraks are only S6. The Krak is an anti-vehicle grenade that has always been balanced to be only truly dangerous to (light) vehicles in larger numbers, giving infantry a chance to mob tanks that got too close and a very, very, very slim one to fight back against a Walker. A single Krak just won't achieve either of those purposes.
Note how you can usually only get ONE Melta bomb on a squad, and have to equip the entire squad with Kraks at 1 pt/model (current Astra Militarum cost) which usually works out to equal or higher cost for the Kraks. In older codices, the cost is higher (Witch Hunters used to get them at 2pts/model).
So yes, Kraks are now stupid and useless. Frags you weren't using in melee anyway, Melta Bombs still work just fine for almost everyone as they only had one in a unit (except those poor Orky Tankbustas... Poor guys had enough issues as it was). Haywires, in all honesty, probably needed a bit of a nerf but I suppose that only really became obvious when cheap Pathfinder units started semi-reliably Glancing 300-400 point Imperial Knights to death.
Good post, put that on the facebook page for the grenades FAQ!