Revisiting Pat Tillman's Friendly Fire

A new investigation has begun, this time criminal, into the "friendly fire" death of Ranger and former football hero, Pat Tillman. According to a New York Times article of March 5, 2006, the investigation is being insituted because the Rangers in the action may have violated military law (i.e., US code). The invesitigation will determine if they "failed to identify their targets before opening fire." If so, this finding would possibly constitute "negligent" homicide and "dereliction of duty."
As a retired Army Ranger, I'd like to make a few salient points:

(1) During the Bush years, only lowly enisted men were ever punished for any offenses.

(2) The Rangers in question were tired, scared, isolated, and probably hungry and cold when they perpetrated this mistake. Certainly, they weren't drinking beers before the shooting.

My question is: Why are they being investigated as described, yet nobody is faulting VP Dick Cheney for the very same offense, (minus the death of his victim)? Why are there different yardsticks for criminality being applied?