Certainly the subject is trolling! No, not really. I would like to make the case that Obliterate is, in almost every case, superior to Chain Reaction:
1. You lose some proc coefficient per target. Basically, your explosion will net you a little more than 1/3 of the APOC and life-on-hit that it used to if you are hitting the same number of targets
1. Damage is more frontloaded, so anything that would be killed by the 2nd or 3rd blast from chain will die sooner
2. The AOE is the same as frost nova, so you can hit everything you freeze with every explosion. Also, this lets you stand well outside of melee range so that things that pop out of freeze for an instant, such as bosses, can still never get a swing off against you, while you can still land all of your DPS. Also note that vs. large crowds, this single fact will largely offset the penalty from the single con of the build. Allow me to demonstrate:
3.14 * 12^2 = 452 sq.yds
3.14 * 18^2 = 1017 sq.yds
That means that you can hit 225% the number of mobs per explosion.
So to recap, you give up some procs from your AE, which is not that bad since most procs are from your whirlwinds/meteors, but you gain +125% more area covered and the ability to stand outside melee range of bosses and things that can unfreeze and smack you briefly.
Give it a shot, I promise you will like it.