Sounds like 343i cranked the AutoAim to max settings =p
Nope
Here is an example. I have always been pretty bad about shooting a jackals arm to get it to show its head in previous games, but in Halo 4 I was popping off head shots on those bastards like there was no tomorrow, one shot in the hand and then one in the head.
I don't know what it is but I can now make twitch shots and everything and I have never been able to do that in Halo 3 or Reach.